This work was supported by Australian Research Council Discovery Project grant (DP180100111 to T.P. and N.E.S), National Health and Medical Research Council Investigator Grant (GNT1175388 to N.E.S.) and Research Fellowship (APP1135928 to T.P.). The authors acknowledge the facilities of Microscopy Australia at the Centre for Advanced Microscopy, Australian National University, a facility that is funded by the University and the Federal Government.

The authors declare no conflicts of interest.

Formaldehyde fixation is a convenient and popular method of achieving rapid in vivo crosslinking of biomolecules10,36,45,46,47,48. Compared to the other potential biomolecule targets, successful capture of translational complexes necessitates an immediate fixation during the snap chilling of the cells or other material. Without the undelayed stabilization, there is a potential for different translation-related processes to continue, shifting the complex distribution away from the unperturbed in vivo state49. Compared to the other methods of translational arrest and ribosomal complex stabilization, the swiftness of formaldehyde action across cell membranes and the indiscriminate nature of the crosslinks promise preservation of the maximal diversity of the translation complex intermediates closer to their natively distributed states50.
The approach presented here has been established and optimized in both yeast and mammalian cells, and methods have now been derived by other groups for use across more diverse biological material, such as in whole vertebrates (e.g., zebrafish embryos)10,38,39,49,51,52. Although these works collectively reassure the versatility and broad applicability of the approach, rapid formaldehyde crosslinking of translational complexes can be considered somewhat difficult to transpose to new types of biological material due to the need of optimizations and adjustments.
A foremost requirement to the success of the method is the re-optimization of the concentration of the formaldehyde and the cell collection and disruption technique. Less permeable, small and round yeast cells require much higher (at least, 10-fold) formaldehyde concentration and physical disruption of the fixed cells. In contrast, large and flattened adherent mammalian cells in culture can be easily over-fixed and require gentle handling upon fixation, while the extraction of the fixed complexes can be performed chemically with membrane disruption using detergents. Under-crosslinking may allow less stable or more short-lived intermediates to dissociate or leak into a later state. Over-crosslinking may negatively affect the ability to isolate and study ribosomal fractions and can create selective biases such as deeper depletion of heavy complexes. In our observation, even minor alterations, such as the type of adherent human cells used, can affect the yield of the recovered crosslinked complexes and may require re-optimization of the crosslinking regimen. We can also anticipate that cells with substantially different permeability properties, such as plant cells, will require additional extensive optimization of the fixation conditions52. Yet, it is difficult to imagine a type of biological material that would be entirely incompatible with the approach.
One consideration pertinent to the mammalian fixation protocol is the density and amount of cell material used as input. It is recommended to have the cells continuously growing without re-seeding or other perturbations for at least 2 days to avoid external influences on cellular translation dynamics. Applicable for most cell types, but for the majority of adherent cells consistently achieved confluence levels of no more than 70% will ensure absence of major contact inhibition effects that can negatively and unpredictably affect translation rates.
Another interesting, and potentially uniquely convenient, feature of formaldehyde fixation stemming from its indiscriminate reactivity is the stabilization effect on translational complexes in systems of mixed taxonomy. Bacterial, and even more so translational complexes of mitochondria, chloroplasts and different intracellular parasites, have been notoriously difficult to target with specific translation inhibitors. In contrast, in the TCP-seq data, footprints mapping to the mitotranscriptome are readily observable in the data38,39,50. An interesting subsequent development could be the use of the approach to investigate translation in entire microcommunities, such as in soil, water or gut samples, where reliable rapid translational arrest and complex stabilization with any other means would be problematic.
It should also be mentioned that for the most complicated material (such as hard and/or bulky tissues), nothing prevents the use of formaldehyde stabilization immediately upon cell disruption and material homogenization. This approach is already frequently employed to remove the cell entry delay when stabilizing translational complexes with specific small molecule inhibitors33,53,54,55. Given that formaldehyde fixation has been traditionally used with excellent results for ex vivo/in vitro sample stabilization in applications such as electron microscopy45,56,57,58, we can expect even less negative effects in this case, particularly those associated with the poor extraction of the translational complexes from the thoroughly fixed cells.
Our findings confirm the usability of rapid formaldehyde fixation to stabilize highly transient complexes, such as those that include eIF4A. It is noteworthy that in contrast to mammals, yeast eIF4A is much more weakly associated with the cap binding complex eIF4F and, as a result, translational complexes in general. eIF4A is usually lost during any extensive purification of the ribosomal material in yeast29,59,60,61,62,63. Yet, in the in vivo-fixed yeast material, it is possible to achieve reliable enrichment of eIF4A in all fractions of translational complexes where its presence would be anticipated. The previously published Sel-TCP-seq data have demonstrated the enrichment of eIF2 and eIF3 that more strongly associate with the ribosomes (but also revealed transiently occurring co-translational protein complex assembly)39. Thus, the method is suitable for the detection of both, stronger and weaker attached constituents of the translational complexes.
To summarize, we have presented an approach useful to gain insights primarily into the changes occurring at the initiation phase of translation and when minimally perturbed ribosomal distribution over the mRNA is required. Importantly, the approach is suitable for the stabilization of relatively labile and dynamic components of translational complexes, such as eIF4A, and can be used broadly subjected to necessary optimizations. We have also provided evidence of the usefulness of formaldehyde fixation in the scenarios of rapid dynamic change of translation, opening up areas of investigation such as fast-paced cellular responses to environmental changes or stress conditions.

Living organisms are subject to dynamic intra- and extracellular changes across their lifespans, which require rapid responses to maintain&#160;homeostasis and ensure survival. To allow environmental adaptation, eukaryotic cells adjust their metabolism via gene expression control. Gene expression control can be exerted during transcription and/or translation; with translational responses generally occurring more rapidly1,2,3,4. For example, translational changes typically arise within 1-30 min of the stress onset, while transcription-level alterations follow hours after stress exposure3,4,5. Alterations to translation output are achieved more rapidly due to the persistent availability of messenger (m)RNA molecules in the cytoplasm. Conversely, at the transcription level, new mRNA molecules must be synthesized, and in eukaryotes, processed and exported from the nucleus, producing extensive delays in the response time2,4,6,7,8.
Acute translational response to stress is generally characterized by an overall decrease in translation output, with the selective upregulation of proteins necessary for cell survival1,3,4,9. Decreasing the protein production output is thought to be crucial due to the high energy expense of the process3,7. To facilitate the selective inhibition and upregulation, translational responses are served by a range of complex regulatory mechanisms. Regulation can be exerted across all phases of translation: initiation, elongation, termination of polypeptide biosynthesis and ribosomal recycling10,11,12,13, but is exhibited most strongly at the initiation phase5,7,9,10,13. During initiation, the small ribosomal subunit (SSU), assisted by eukaryotic initiation factors (eIFs), binds to, and scans the 5&#39; untranslated region (UTR) of mRNA until a start codon is recognized2,5,6,8,11,12,13. Regulatory mechanisms often target eIFs affecting attachment, scanning, and start codon recognition. For example, the initiation factor eIF2, an essential translation factor that aids in the recruitment of an initiator Met-tRNAiMet to the SSU, is often targeted in eukaryotes under stress conditions4,6,11. In yeast, phosphorylation of this factor can be induced under nutrient deprivation and osmotic stress1,4,11,14,15, and in mammalian cells, amino acid starvation, endoplasmic reticulum (ER) stress, UV stress, viral infection, and altered oxygen levels may trigger this response8,9,11. Rapid upregulation of specific mRNA translation is evident in the mammalian cell response to hypoxia, which exhibits a global rapid translation inhibition and selective upregulation of hypoxia-inducible factors (HIFs) biosynthesis. HIFs are transcription factors, which then elicit longer term cellular reprogramming at the DNA transcription level8,9,16. Similar responses have been observed in yeast under heat stress, with rapid translational expression of Heat Shock Proteins (HSPs) followed by delayed transcription-level responses17,18. In addition to nutrient deprivation and heat shock, translational responses in yeast have been studied under varying oxygen8,19, salinity5, phosphate, sulfur20,21 and nitrogen22,23 levels. This research has widespread implications for the industrial uses of yeast, such as baking and fermentation24,25. Translational responses may also be instrumental in furthering understanding of diseases such as neurodegenerative disorders and heart disease, that are characterized by intracellular stresses like oxidative stress. Overall, translational responses are integral to the gene expression control and facilitate rapid adaptation to a broad range of stress conditions in eukaryotic organisms.
In order to study translational responses, methods are required that provide minimally distorted snapshots of the translation landscape. Polysome profiling is a classical approach used in the study of translation across mRNA, involving the separation of poly(ribo)somal fractions of mRNA via ultracentrifugation through sucrose gradients26,27. The approach may be used to explore levels of translation for individual mRNAs (with the detection methods such as reverse transcription and polymerase chain reaction, RT-PCR26), or globally in conjunction with high-throughput techniques (microarray or RNA-seq28,29). A more evolved approach is ribosome profiling, that allows the study of positions of elongating ribosomes along an mRNA molecule at a genome-wide scale, as well as the inference of efficiency of translation across transcriptome and utilization of the main and alternative start sites30,31. Ribosome profiling involves the isolation and sequencing of mRNA fragments protected by ribosomal presence over them. Ribosome profiling has provided considerable insight into translation dynamics across a number of conditions, including hypoxic stress, heat shock and oxidative stress31,32. The technique has been adapted to multiple source material types, including yeast and mammalian cells.
While polysome and ribosome profiling have been fundamental in extending the capabilities of research in translation, the process of translation includes various translational intermediates and complexes that are difficult to capture with these methods11,13. An additional limitation stems from the lack of ability to study rapid response types, as translational complexes are either stabilized in vivo by the addition of specific translation inhibitors (antibiotics), leading to certain ribosome distribution artifacts, or ex vivo upon cell lysis specifically (antibiotics) or unspecifically (high salt or magnesium ions), leading to the deprivation of the shorter-lived or less stable intermediates33,34,35.
Formaldehyde is widely used to crosslink nucleic acids and proteins, such as in chromatin immunoprecipitation (ChIP) and crosslinking immunoprecipitation (CLIP) studies. Its small size and excellent cell permeability allow for a rapid in vivo action36. Based on the rapid formaldehyde crosslinking, the ribosome profiling approach has been extended with the Translation Complex Profile Sequencing (TCP-seq)10,36,37,38,39,40. TCP-seq, first developed in yeast, allows the capture of all translation intermediates, including scanning or post-termination SSU complexes and multiple ribosomal configurations37,38,41,42. The method has been utilized in several studies10,38,39,41,42, some of which use a combinatory approach of both translation inhibitors and formaldehyde crosslinking to facilitate the arrest of translation. A further modified version of the technique, selective TCP-seq39, has recently been employed to include immunopurification of the crosslinked complexes, broadening the scope of the TCP-seq applications. The rapid, efficient and reversible nature of formaldehyde crosslinking makes these approaches suitable for studying transient mRNA:translation complex interactions, particularly in the context of highly dynamic translation-level response pathways.
Here we detail the processes of in vivo formaldehyde crosslinking for the purpose of comprehensive translation complex stabilization and isolation. We provide separate protocols nuanced for yeast and mammalian cells (Figure 1). We further outline examples of the subsequent use of the crosslink-stabilized material (Figure 1), such as for co-purified protein factor detection using immunoblotting (western-blotting), immuno-assisted purification (or &#39;immunoprecipitation&#39;; IP) and enrichment of translational complexes containing specific factors of interest, electron microscopy and RNA sequencing.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/62639/62639fig01.jpg" /> 
Figure 1: Schematic depicting an overview of the typical experimental setup. Main steps of in vivo formaldehyde stabilization of translational complexes are depicted as a flowchart, supplemented by information about the key necessary instruments. Potential downstream applications of the crosslinked material are outlined, including examples which have been successfully employed but not directly covered in this protocol, such as SPRI bead purification of RNA, RNA sequencing, and mass-spectrometry. <a href="https://www.jove.com/files/ftp_upload/62639/62639fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Yeast extract</td>
			<td>Merck, Sigma-Aldrich</td>
			<td>70161</td>
			<td></td>
		</tr>
		<tr>
			<td>Peptone</td>
			<td>Merck, Sigma-Aldrich</td>
			<td>70178</td>
			<td></td>
		</tr>
		<tr>
			<td>D-Glucose (Dextrose)</td>
			<td>Merck, Sigma-Aldrich</td>
			<td>49139</td>
			<td></td>
		</tr>
		<tr>
			<td>Adenine sulphate</td>
			<td>Amresco</td>
			<td>0607-50G</td>
			<td></td>
		</tr>
		<tr>
			<td>Formaldehyde solution</td>
			<td>Merck Sigma-Aldrich</td>
			<td>F11635-500ML</td>
			<td>ACS reagent, 37&#160;wt. % in H2O, contains 10-15% Methanol as stabiliser (to prevent polymerisation)</td>
		</tr>
		<tr>
			<td>RNaseOUT&#8482; Recombinant Ribonuclease Inhibitor</td>
			<td>Invitrogen&#8482; byThermo Fischer Scientific</td>
			<td>10777019</td>
			<td></td>
		</tr>
		<tr>
			<td>cOmplete&#8482;, EDTA-free Protease Inhibitor Cocktail</td>
			<td>COEDTAF-RO Roche by Merck</td>
			<td>11873580001</td>
			<td></td>
		</tr>
		<tr>
			<td>Magnesium chloride solution</td>
			<td>(Merck/Sigma-Aldrich)</td>
			<td>M1028</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethylenediaminetetraacetic acid solution</td>
			<td>(Merck/Sigma-Aldrich)</td>
			<td>E7889</td>
			<td></td>
		</tr>
		<tr>
			<td>Ambion&#8482; RNase I, cloned, 100 U/&#181;L</td>
			<td>Ambion</td>
			<td>AM2294</td>
			<td></td>
		</tr>
		<tr>
			<td>SUPERase&#8226;In&#8482; RNase Inhibitor (20 U/&#956;L)</td>
			<td>Invitrogen&#8482; by Thermo Fisher Scientific</td>
			<td>AM2694</td>
			<td></td>
		</tr>
		<tr>
			<td>Acidic phenol:chlorophorm:isoamyl alcohol 125:24:1 (pH 4.0-5.0)</td>
			<td>(Merck/Sigma-Aldrich)</td>
			<td>P1944-100ML</td>
			<td></td>
		</tr>
		<tr>
			<td>Dynabeads&#8482; Goat Anti-Mouse IgG</td>
			<td>Invitrogen&#8482; by Thermo Fisher Scientific)</td>
			<td>11033</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Acetate (3 M), pH 5.5</td>
			<td>Invitrogen&#8482; by Thermo Fisher Scientific)</td>
			<td>AM9740</td>
			<td></td>
		</tr>
		<tr>
			<td>Glycogen (5 mg/ml)</td>
			<td>Invitrogen&#8482; by Thermo Fisher Scientific)</td>
			<td>AM9510</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethyl alcohol, Pure</td>
			<td>Merck; Sigma Aldrich</td>
			<td>E7023</td>
			<td></td>
		</tr>
		<tr>
			<td>Amersham&#8482;&#160;Hybond&#174; P Western blotting membranes, PVDF</td>
			<td>Merck</td>
			<td>GE10600023</td>
			<td>PVDF membrane for western blotting</td>
		</tr>
		<tr>
			<td>Bolt&#8482; 4 to 12%, Bis-Tris, 1.0 mm, Mini Protein Gel</td>
			<td>Invitrogen&#8482; by ThermoFischer Sientific</td>
			<td>NW04120BOX</td>
			<td>Protein gel</td>
		</tr>
		<tr>
			<td>4X Bolt&#8482; LDS Sample Buffer</td>
			<td>Invitrogen&#8482; by ThermoFischer Sientific</td>
			<td>B0007</td>
			<td>&#160;LDS sample loading buffer</td>
		</tr>
		<tr>
			<td>Precision Plus Protein&#8482; Kaleidoscope&#8482; Prestained Protein Standards</td>
			<td>BioRad</td>
			<td>1610375</td>
			<td>Protein ladder</td>
		</tr>
		<tr>
			<td>20X Bolt&#8482; MES SDS Running Buffer</td>
			<td>ThermoFischer Scientific</td>
			<td>B0002</td>
			<td>PAGE runninjg buffer</td>
		</tr>
		<tr>
			<td>Intercept&#174; (PBS) Blocking Buffer</td>
			<td>LI-COR</td>
			<td>927-70001</td>
			<td>Odyssey Blcoking buffer (PBS)</td>
		</tr>
		<tr>
			<td>IRDye&#174; 800CW Goat anti-Mouse IgG Secondary Antibody</td>
			<td>LI-COR</td>
			<td>92632210</td>
			<td></td>
		</tr>
		<tr>
			<td>IRDye&#174; 800CW Goat anti-Rabbit IgG Secondary Antibody</td>
			<td>LI-COR</td>
			<td>92632211</td>
			<td></td>
		</tr>
		<tr>
			<td>TAP Tag Polyclonal Antibody</td>
			<td>Invitrogen&#8482; by ThermoFischer Sientific</td>
			<td>CAB1001</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti-beta Actin antibody</td>
			<td>Abcam</td>
			<td>ab8227</td>
			<td></td>
		</tr>
		<tr>
			<td>Sucrose</td>
			<td>(Merck/Sigma-Aldrich)</td>
			<td>84097</td>
			<td>BioUltra, for molecular biology, &#8805;99.5% (HPLC)</td>
		</tr>
		<tr>
			<td>DL-Dithiothreitol solution</td>
			<td>(Merck/Sigma-Aldrich)</td>
			<td>43816</td>
			<td>BioUltra, for molecular biology, ~1 M in H2O</td>
		</tr>
		<tr>
			<td>Terumo Syringe 1CC/mL</td>
			<td>Terumo Syringe</td>
			<td>878499</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium chloride</td>
			<td>(Merck/Sigma-Aldrich)</td>
			<td>60128</td>
			<td></td>
		</tr>
		<tr>
			<td>HEPES</td>
			<td>(Merck/Sigma-Aldrich)</td>
			<td>H3375</td>
			<td></td>
		</tr>
		<tr>
			<td>Dulbecco&#39;s Modified Eagle&#39;s Medium - high glucose</td>
			<td>Sigma Aldrich</td>
			<td>D5796</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal Bovine Serum</td>
			<td>Sigma Aldrich</td>
			<td>12003C</td>
			<td></td>
		</tr>
		<tr>
			<td>Trypsin-EDTA (0.05%), phenol red</td>
			<td>Gibco</td>
			<td>25300062</td>
			<td></td>
		</tr>
		<tr>
			<td>Dulbecco&#39;s Phosphate Buffered Saline with Calcium and magnesium</td>
			<td>Sigma-Aldrich</td>
			<td>D8662</td>
			<td></td>
		</tr>
		<tr>
			<td>Glycine</td>
			<td>Sigma-Aldrich</td>
			<td>G7126</td>
			<td></td>
		</tr>
		<tr>
			<td>Tris hydrochloride</td>
			<td>Merck/Sigma-Aldrich</td>
			<td>10812846001</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium dodecyl sulfate</td>
			<td>Merck/Sigma-Aldrich</td>
			<td>436143</td>
			<td></td>
		</tr>
		<tr>
			<td>IGEPAL CA-630</td>
			<td>Merck/Sigma-Aldrich</td>
			<td>I3021</td>
			<td></td>
		</tr>
		<tr>
			<td>Rnasin Ribonuclease Inhibitor</td>
			<td>Promega</td>
			<td>N2111</td>
			<td></td>
		</tr>
		<tr>
			<td>Stainless steel grinding jar</td>
			<td>Retsch</td>
			<td>02.462.0059</td>
			<td></td>
		</tr>
		<tr>
			<td>MM400 mixer mill</td>
			<td>Retsch</td>
			<td>20.745.0001</td>
			<td></td>
		</tr>
		<tr>
			<td>Gradient Fractionator</td>
			<td>Brandel</td>
			<td>BRN-BR-188</td>
			<td></td>
		</tr>
		<tr>
			<td>Thermomixer R</td>
			<td>Eppendorf</td>
			<td>Z605271</td>
			<td></td>
		</tr>
		<tr>
			<td>Nanodrop spectrophotometer</td>
			<td>Thermo Fisher Scientific</td>
			<td>ND-2000</td>
			<td></td>
		</tr>
		<tr>
			<td>0.5-ml microcentrifuge tubes with locking devices</td>
			<td>Eppendorf Safe-Lock</td>
			<td>30121023</td>
			<td></td>
		</tr>
		<tr>
			<td>Mini Gel Tank</td>
			<td>(Thermo Fisher Scientific)</td>
			<td>A25977</td>
			<td>PAGE running tank</td>
		</tr>
		<tr>
			<td>5 mL, Open-Top Thinwall Ultra-Clear Tube, 13 x 51mm</td>
			<td>Beckman-Coulter</td>
			<td>344057</td>
			<td></td>
		</tr>
		<tr>
			<td>13.2 mL, Certified Free Open-Top Thinwall Polypropylene, 14 x 89mm - 50Pk</td>
			<td>Beckman-Coulter</td>
			<td>331372</td>
			<td></td>
		</tr>
		<tr>
			<td>Amicon Ultra-0.5 ultrafiltration devices</td>
			<td>Merck</td>
			<td>UFC5030</td>
			<td>Ultracel-30 regenerated cellulose membrane, 0.5 mL sample volume</td>
		</tr>
		<tr>
			<td>Thermo Sorvall Evolution RC Floor Super Speed Centrifuge</td>
			<td>Cambridge Scientific</td>
			<td>15566</td>
			<td></td>
		</tr>
		<tr>
			<td>Beckman Coulter Optima L-90K</td>
			<td>GMI</td>
			<td>8043-30-1191</td>
			<td></td>
		</tr>
		<tr>
			<td>Nunc EasYFlask 175cm2</td>
			<td>Thermofisher Scientific</td>
			<td>159910</td>
			<td></td>
		</tr>
		<tr>
			<td>Falcon 50 mL Conical Centrifuge Tubes</td>
			<td>Thermofisher Scientific</td>
			<td>14-432-22</td>
			<td></td>
		</tr>
		<tr>
			<td>25 mL Serological Pipette</td>
			<td>Sigma-Aldrich</td>
			<td>SIAL1250</td>
			<td></td>
		</tr>
		<tr>
			<td>10 mL Serological Pipette</td>
			<td>Sigma-Aldrich</td>
			<td>SIAL1100</td>
			<td></td>
		</tr>
		<tr>
			<td>DNA lobind tubes</td>
			<td>Eppendorf</td>
			<td>30108051</td>
			<td></td>
		</tr>
		<tr>
			<td>Cold Centrifuge 5810 R</td>
			<td>Eppendorf</td>
			<td>EP022628188</td>
			<td>for 50 mL tubes</td>
		</tr>
		<tr>
			<td>Orbital Shaking Incubator</td>
			<td>Ratek</td>
			<td>OM11</td>
			<td></td>
		</tr>
		<tr>
			<td>Frezco 17 Microcentrifuge</td>
			<td>Thermofisher Scientific</td>
			<td>75002402</td>
			<td></td>
		</tr>
		<tr>
			<td>Eppendorf DNA lo-bind tubes</td>
			<td>Merck/Sigma-Aldrich</td>
			<td>EP0030108051</td>
			<td></td>
		</tr>
		<tr>
			<td>Eppendorf&#174; Protein LoBind tubes</td>
			<td>Merck/Sigma-Aldrich</td>
			<td>EP0030108116</td>
			<td></td>
		</tr>
		<tr>
			<td>SW 41 Ti Swinging bucket rotor</td>
			<td>Beckman-Coulter</td>
			<td>331362</td>
			<td></td>
		</tr>
		<tr>
			<td>Heracell&#8482; 150i CO2 Incubator, 150 L</td>
			<td>Thermofisher Scientific</td>
			<td>51026282</td>
			<td></td>
		</tr>
		<tr>
			<td>0,3 mL ultra-fine II short insulin syringe</td>
			<td>BD Medical</td>
			<td>328822</td>
			<td></td>
		</tr>
		<tr>
			<td>3 mL syringe with Luer Lok tip</td>
			<td>BD Medical</td>
			<td>302113</td>
			<td></td>
		</tr>
		<tr>
			<td>25 G x 16 mm Hypodermic Needle</td>
			<td>Terumo</td>
			<td>TUAN2516R1</td>
			<td></td>
		</tr>
	</tbody>
</table>

rapid in vivo fixation and isolation of translational complexes from eukaryotic cells

Rapid responses involving fast redistribution of messenger(m)RNA and alterations of mRNA translation are pertinent to ongoing homeostatic adjustments of the cells. These adjustments are critical to eukaryotic cell survivability and &#39;damage control&#39; during fluctuating nutrient and salinity levels, temperature, and various chemical and radiation stresses. Due to the highly dynamic nature of the RNA-level responses, and the instability of many of the RNA:RNA and RNA:protein intermediates, obtaining a meaningful snapshot of the cytoplasmic RNA state is only possible with a limited number of methods. Transcriptome-wide, RNA-seq-based ribosome profiling-type experiments are among the most informative sources of data for the control of translation. However, absence of a uniform RNA and RNA:protein intermediate stabilization can lead to different biases, particularly in the fast-paced cellular response pathways. In this article, we provide a detailed protocol of rapid fixation applicable to eukaryotic cells of different permeability, to aid in RNA and RNA:protein intermediate stabilization. We further provide examples of isolation of the stabilized RNA:protein complexes based on their co-sedimentation with ribosomal and poly(ribo)somal fractions. The separated stabilized material can be subsequently used as part of ribosome profiling-type experiments, such as in Translation Complex Profile sequencing (TCP-seq) approach and its derivatives. Versatility of the TCP-seq-style methods has now been demonstrated by the applications in a variety of organisms and cell types. The stabilized complexes can also be additionally affinity-purified and imaged using electron microscopy, separated into different poly(ribo)somal fractions and subjected to RNA sequencing, owing to the ease of the crosslink reversal. Therefore, methods based on snap-chilling and formaldehyde fixation, followed by the sedimentation-based or other type of RNA:protein complex enrichment, can be of particular interest in investigating finer details of rapid RNA:protein complex dynamics in live cells.

Watch this Scientific Journal Video about Rapid In Vivo Fixation and Isolation of Translational Complexes from Eukaryotic Cells at JoVE.com

Rapid In Vivo Fixation and Isolation of Translational Complexes from Eukaryotic Cells

We present a technique to rapidly stabilize translational (protein biosynthesis) complexes with formaldehyde crosslinking in live yeast and mammalian cells. The approach enables dissecting transient intermediates and dynamic RNA:protein interactions. The crosslinked complexes can be used in multiple downstream applications such as in deep sequencing-based profiling methods, microscopy, and mass-spectrometry.

Rapid In Vivo Fixation and Isolation of Translational Complexes from Eukaryotic Cells

Rapid responses involving fast redistribution of messenger(m)RNA and alterations of mRNA translation are pertinent to ongoing homeostatic adjustments of ...

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3.8K Views.  The Australian National University. We present a technique to rapidly stabilize translational (protein biosynthesis) complexes with formaldehyde crosslinking in live yeast and mammalian cells. The approach enables dissecting transient intermediates and dynamic RNA:protein interactions. The crosslinked complexes can be used in multiple downstream applications such as in deep sequencing-based profiling methods, microscopy, and mass-spectrometry.

Video: Rapid In Vivo Fixation and Isolation of Translational Complexes from Eukaryotic Cells

Isolation of Labile Multi-protein Complexes by in vivo Controlled Cellular Cross-Linking and Immuno-magnetic Affinity Chromatography

The dynamic nature of cellular machineries is frequently built on transient and/or weak protein associations. These low affinity interactions preclude stringent methods for the isolation and identification of protein networks around a protein of interest. The use of chemical crosslinkers allows the selective stabilization of labile interactions, thus bypassing biochemical limitations for purification. Here we present a protocol amenable for cells in culture that uses a homobifunctional crosslinker with a spacer arm of 12 &Aring;, dithiobis-(succinimidyl proprionate) (DSP). DSP is cleaved by reduction of a disulphide bond present in the molecule. Cross-linking combined with immunoaffinity chromatography of proteins of interest with magnetic beads allows the isolation of protein complexes that otherwise would not withstand purification. This protocol is compatible with regular western blot techniques and it can be scaled up for protein identification by mass spectrometry1.
Stephanie A. Zlatic and Pearl V. Ryder contributed equally to this work.

Isolation of Labile Multi-protein Complexes by in vivo Controlled Cellular Cross-Linking and Immuno-magnetic Affinity Chromatography

The cell permeable crosslinker DSP [dithiobis-(succinimidyl propionate)] stabilizes transient and labile interactions in vivo, which allows their isolation using stringent protein complex purification techniques. Here we present a technique for crosslinking cells grown in culture followed by isolation of protein complexes by immunoprecipitation.

The dynamic nature of cellular machineries is frequently built on transient and/or weak protein associations. These low affinity interactions preclude ...

Establishment of Microbial Eukaryotic Enrichment Cultures from a Chemically Stratified Antarctic Lake and Assessment of Carbon Fixation Potential

Lake Bonney is one of numerous permanently ice-covered lakes located in the McMurdo Dry Valleys, Antarctica. The perennial ice cover maintains a chemically stratified water column and unlike other inland bodies of water, largely prevents external input of carbon and nutrients from streams. Biota are exposed to numerous environmental stresses, including year-round severe nutrient deficiency, low temperatures, extreme shade, hypersalinity, and 24-hour darkness during the winter 1. These extreme environmental conditions limit the biota in Lake Bonney almost exclusively to microorganisms 2.
Single-celled microbial eukaryotes (called "protists") are important players in global biogeochemical cycling 3 and play important ecological roles in the cycling of carbon in the dry valley lakes, occupying both primary and tertiary roles in the aquatic food web. In the dry valley aquatic food web, protists that fix inorganic carbon (autotrophy) are the major producers of organic carbon for organotrophic organisms 4, 2. Phagotrophic or heterotrophic protists capable of ingesting bacteria and smaller protists act as the top predators in the food web 5. Last, an unknown proportion of the protist population is capable of combined mixotrophic metabolism 6, 7. Mixotrophy in protists involves the ability to combine photosynthetic capability with phagotrophic ingestion of prey microorganisms. This form of mixotrophy differs from mixotrophic metabolism in bacterial species, which generally involves uptake dissolved carbon molecules. There are currently very few protist isolates from permanently ice-capped polar lakes, and studies of protist diversity and ecology in this extreme environment have been limited 8, 4, 9, 10, 5. A better understanding of protist metabolic versatility in the simple dry valley lake food web will aid in the development of models for the role of protists in the global carbon cycle.
We employed an enrichment culture approach to isolate potentially phototrophic and mixotrophic protists from Lake Bonney. Sampling depths in the water column were chosen based on the location of primary production maxima and protist phylogenetic diversity 4, 11, as well as variability in major abiotic factors affecting protist trophic modes: shallow sampling depths are limited for major nutrients, while deeper sampling depths are limited by light availability. In addition, lake water samples were supplemented with multiple types of growth media to promote the growth of a variety of phototrophic organisms.
RubisCO catalyzes the rate limiting step in the Calvin Benson Bassham (CBB) cycle, the major pathway by which autotrophic organisms fix inorganic carbon and provide organic carbon for higher trophic levels in aquatic and terrestrial food webs 12. In this study, we applied a radioisotope assay modified for filtered samples 13 to monitor maximum carboxylase activity as a proxy for carbon fixation potential and metabolic versatility in the Lake Bonney enrichment cultures.

Microbial eukaryotes are both a source of photosynthetically-derived carbon and top predatory species in permanently ice-covered Antarctic lakes. This report describes an enrichment culture approach to isolate metabolically versatile microbial eukaryotes from the Antarctic lake, Lake Bonney, and assesses inorganic carbon fixation potential using a radioisotope assay for Ribulose-1,5-bisphophate carboxylase oxygenase (RubisCO) activity.

Lake Bonney is one of numerous permanently ice-covered lakes located in the McMurdo Dry Valleys, Antarctica. The perennial ice cover maintains a ...

Isolation of Ribosome Bound Nascent Polypeptides in vitro to Identify Translational Pause Sites Along mRNA

The rate of translational elongation is non-uniform. mRNA secondary structure, codon usage and mRNA associated proteins may alter ribosome movement on the messagefor review see 1. However, it's now widely accepted that synonymous codon usage is the primary cause of non-uniform translational elongation rates1. Synonymous codons are not used with identical frequency. A bias exists in the use of synonymous codons with some codons used more frequently than others2. Codon bias is organism as well as tissue specific2,3. Moreover, frequency of codon usage is directly proportional to the concentrations of cognate tRNAs4. Thus, a frequently used codon will have higher multitude of corresponding tRNAs, which further implies that a frequent codon will be translated faster than an infrequent one. Thus, regions on mRNA enriched in rare codons (potential pause sites) will as a rule slow down ribosome movement on the message and cause accumulation of nascent peptides of the respective sizes5-8. These pause sites can have functional impact on the protein expression, mRNA stability and protein foldingfor review see 9. Indeed, it was shown that alleviation of such pause sites can alter ribosome movement on mRNA and subsequently may affect the efficiency of co-translational (in vivo) protein folding1,7,10,11. To understand the process of protein folding in vivo, in the cell, that is ultimately coupled to the process of protein synthesis it is essential to gain comprehensive insights into the impact of codon usage/tRNA content on the movement of ribosomes along mRNA during translational elongation.
Here we describe a simple technique that can be used to locate major translation pause sites for a given mRNA translated in various cell-free systems6-8. This procedure is based on isolation of nascent polypeptides accumulating on ribosomes during in vitro translation of a target mRNA. The rationale is that at low-frequency codons, the increase in the residence time of the ribosomes results in increased amounts of nascent peptides of the corresponding sizes. In vitro transcribed mRNA is used for in vitro translational reactions in the presence of radioactively labeled amino acids to allow the detection of the nascent chains. In order to isolate ribosome bound nascent polypeptide complexes the translation reaction is layered on top of 30% glycerol solution followed by centrifugation. Nascent polypeptides in polysomal pellet are further treated with ribonuclease A and resolved by SDS PAGE. This technique can be potentially used for any protein and allows analysis of ribosome movement along mRNA and the detection of the major pause sites. Additionally, this protocol can be adapted to study factors and conditions that can alter ribosome movement and thus potentially can also alter the function/conformation of the protein.

Isolation of Ribosome Bound Nascent Polypeptides in vitro to Identify Translational Pause Sites Along mRNA

A technique to identify translational pause sites on mRNA is described. This procedure is based on isolation of nascent polypeptides accumulating on ribosomes during in vitro translation of a target mRNA, followed by the size analysis of the nascent chains using a denaturing gel electrophoresis.

The rate of translational elongation is non-uniform. mRNA secondary structure, codon usage and mRNA associated proteins may alter ribosome movement on the ...

Efficient and Rapid Isolation of Early-stage Embryos from Arabidopsis thaliana Seeds

In flowering plants, the embryo develops within a nourishing tissue - the endosperm - surrounded by the maternal seed integuments (or seed coat). As a consequence, the isolation of plant embryos at early stages (1 cell to globular stage) is technically challenging due to their relative inaccessibility. Efficient manual dissection at early stages is strongly impaired by the small size of young Arabidopsis seeds and the adhesiveness of the embryo to the surrounding tissues. Here, we describe a method that allows the efficient isolation of young Arabidopsis embryos, yielding up to 40 embryos in 1 hr to 4 hr, depending on the downstream application. Embryos are released into isolation buffer by slightly crushing 250-750 seeds with a plastic pestle in an Eppendorf tube. A glass microcapillary attached to either a standard laboratory pipette (via a rubber tube) or a hydraulically controlled microinjector is used to collect embryos from droplets placed on a multi-well slide on an inverted light microscope. The technical skills required are simple and easily transferable, and the basic setup does not require costly equipment. Collected embryos are suitable for a variety of downstream applications such as RT-PCR, RNA sequencing, DNA methylation analyses, fluorescence in situ hybridization (FISH), immunostaining, and reporter gene assays.

Efficient and Rapid Isolation of Early-stage Embryos from Arabidopsis thaliana Seeds

We report an efficient and simple method to isolate embryos at early stages of development from Arabidopsis thaliana seeds. Up to 40 embryos can be isolated in 1 hr to 4 hr, depending on the downstream application. The procedure is suitable for transcriptome, DNA methylation, reporter gene expression, immunostaining and fluorescence in situ hybridization analyses.

In flowering plants, the embryo develops within a nourishing tissue - the endosperm - surrounded by the maternal seed integuments (or seed coat). As a ...

Identification of Post-translational Modifications of Plant Protein Complexes

Plants adapt quickly to changing environments due to elaborate perception and signaling systems. During pathogen attack, plants rapidly respond to infection via the recruitment and activation of immune complexes. Activation of immune complexes is associated with post-translational modifications (PTMs) of proteins, such as phosphorylation, glycosylation, or ubiquitination. Understanding how these PTMs are choreographed will lead to a better understanding of how resistance is achieved.
Here we describe a protein purification method for nucleotide-binding leucine-rich repeat (NB-LRR)-interacting proteins and the subsequent identification of their post-translational modifications (PTMs). With small modifications, the protocol can be applied for the purification of other plant protein complexes. The method is based on the expression of an epitope-tagged version of the protein of interest, which is subsequently partially purified by immunoprecipitation and subjected to mass spectrometry for identification of interacting proteins and PTMs.
This protocol demonstrates that: i). Dynamic changes in PTMs such as phosphorylation can be detected by mass spectrometry; ii). It is important to have sufficient quantities of the protein of interest, and this can compensate for the lack of purity of the immunoprecipitate; iii). In order to detect PTMs of a protein of interest, this protein has to be immunoprecipitated to get a sufficient quantity of protein.

We describe here a protocol for the purification and characterization of plant protein complexes. We demonstrate that by immunoprecipitating a single protein within a complex, so we can identify its post-translational modifications and its interacting partners.

Plants adapt quickly to changing environments due to elaborate perception and signaling systems. During pathogen attack, plants rapidly respond to ...

An in vivo Crosslinking Approach to Isolate Protein Complexes From Drosophila Embryos

Many cellular processes are controlled by multisubunit protein complexes. Frequently these complexes form transiently and require native environment to assemble. Therefore, to identify these functional protein complexes, it is important to stabilize them in vivo before cell lysis and subsequent purification. Here we describe a method used to isolate large bona fide protein complexes from Drosophila embryos. This method is based on embryo permeabilization and stabilization of the complexes inside the embryos by in vivo crosslinking using a low concentration of formaldehyde, which can easily cross the cell membrane. Subsequently, the protein complex of interest is immunopurified followed by gel purification and analyzed by mass spectrometry. We illustrate this method using purification of a Tudor protein complex, which is essential for germline development. Tudor is a large protein, which contains multiple Tudor domains - small modules that interact with methylated arginines or lysines of target proteins. This method can be adapted for isolation of native protein complexes from different organisms and tissues.

An in vivo Crosslinking Approach to Isolate Protein Complexes From Drosophila Embryos

Multi-component protein complexes play crucial roles during cellular function and development. Here we describe a method used to isolate native protein complexes from Drosophila embryos after in vivo crosslinking followed by purification of the crosslinked complexes for subsequent structure-function analysis.

Many cellular processes are controlled by multisubunit protein complexes. Frequently these complexes form transiently and require native environment to ...

Isolation and Functional Analysis of Mitochondria from Cultured Cells and Mouse Tissue

Comparison between two or more distinct groups, such as healthy vs. disease, is necessary to determine cellular status. Mitochondria are at the nexus of cell heath due to their role in both cell metabolism and energy production as well as control of apoptosis. Therefore, direct evaluation of isolated mitochondria and mitochondrial perturbation offers the ability to determine if organelle-specific (dys)function is occurring. The methods described in this protocol include isolation of intact, functional mitochondria from HEK cultured cells and mouse liver and spinal cord, but can be easily adapted for use with other cultured cells or animal tissues. Mitochondrial function assessed by TMRE and the use of common mitochondrial uncouplers and inhibitors in conjunction with a fluorescent plate reader allow this protocol not only to be versatile and accessible to most research laboratories, but also offers high throughput.

Comparison of mitochondrial membrane potential between samples yields valuable information about cellular status. Detailed steps for isolating mitochondria and assessing response to inhibitors and uncouplers using fluorescence are described. The method and utility of this protocol are illustrated by use of a cell culture and animal model of cellular stress.

Comparison between two or more distinct groups, such as healthy vs. disease, is necessary to determine cellular status. Mitochondria are at the nexus of ...

Isolation and Primary Culture of Mouse Aortic Endothelial Cells

The vascular endothelium is essential to normal vascular homeostasis. Its dysfunction participates in various cardiovascular disorders. The mouse is an important model for cardiovascular disease research. This study demonstrates a simple method to isolate and culture endothelial cells from the mouse aorta without any special equipment. To isolate endothelial cells, the thoracic aorta is quickly removed from the mouse body, and the attached adipose tissue and connective tissue are removed from the aorta. The aorta is cut into 1 mm rings. Each aortic ring is opened and seeded onto a growth factor reduced matrix with the endothelium facing down. The segments are cultured in endothelial cell growth medium for about 4 days. The endothelial sprouting starts as early as day 2. The segments are then removed and the cells are cultured continually until they reach confluence. The endothelial cells are harvested using neutral proteinase and cultured in endothelial cell growth medium for another two passages before being used for experiments. Immunofluorescence staining indicated that after the second passage the majority of cells were double positive for Dil-ac-LDL uptake, Lectin binding, and CD31 staining, the typical characteristics of endothelial cells. It is suggested that cells at the second to third passages are suitable for in vitro and in vivo experiments to study the endothelial biology. Our protocol provides an effective means of identifying specific cellular and molecular mechanisms in endothelial cell physiopathology.

The vascular endothelial cells play a significant role in many important cardiovascular disorders. This article describes a simple method to isolate and expand endothelial cells from the mouse aorta without using any special equipment. Our protocol provides an effective means of identifying mechanisms in endothelial cell physiopathology.

The vascular endothelium is essential to normal vascular homeostasis. Its dysfunction participates in various cardiovascular disorders. The mouse is an ...

Genome-wide Purification of Extrachromosomal Circular DNA from Eukaryotic Cells

Extrachromosomal circular DNAs (eccDNAs) are common genetic elements in Saccharomyces cerevisiae and are reported in other eukaryotes as well. EccDNAs contribute to genetic variation among somatic cells in multicellular organisms and to evolution of unicellular eukaryotes. Sensitive methods for detecting eccDNA are needed to clarify how these elements affect genome stability and how environmental and biological factors&#160;induce their formation in eukaryotic cells. This video presents a sensitive eccDNA-purification method called Circle-Seq. The method encompasses column purification of circular DNA, removal of remaining linear chromosomal DNA, rolling-circle amplification of eccDNA, deep sequencing, and mapping. Extensive exonuclease treatment&#160;was&#160;required for sufficient linear chromosomal DNA degradation. The rolling-circle amplification step by &#966;29 polymerase enriched for circular DNA over linear DNA. Validation of the Circle-Seq method on three S. cerevisiae CEN.PK populations of 1010 cells detected hundreds of eccDNA profiles in sizes larger than 1 kilobase. Repeated findings of ASP3-1, COS111, CUP1, RSC30,&#160;HXT6, HXT7 genes on circular DNA in both S288c and CEN.PK suggests that DNA circularization is conserved between strains at these loci. In sum, the Circle-Seq method has broad applicability for genome-scale screening for eccDNA in eukaryotes as well as for detecting specific eccDNA types.

This paper presents a sensitive method called Circle-Seq for purifying extrachromosomal circular DNA (eccDNA). The method encompasses column purification, removal of remaining linear chromosomal DNA, rolling-circle amplification and high-throughput sequencing. Circle-Seq is applicable to genome-scale screening of eukaryotic eccDNA and studying genome instability and copy-number variation.

Extrachromosomal circular DNAs (eccDNAs) are common genetic elements in Saccharomyces cerevisiae and are reported in other eukaryotes as well. EccDNAs ...

Filtration Isolation of Nucleic Acids:  A Simple and Rapid DNA Extraction Method

FINA, filtration isolation of nucleic acids, is a novel extraction method which utilizes vertical filtration via a separation membrane and absorbent pad to extract cellular DNA from whole blood in less than 2 min. The blood specimen is treated with detergent, mixed briefly and applied by pipet to the separation membrane. The lysate wicks into the blotting pad due to capillary action, capturing the genomic DNA on the surface of the separation membrane. The extracted DNA is retained on the membrane during a simple wash step wherein PCR inhibitors are wicked into the absorbent blotting pad. The membrane containing the entrapped DNA is then added to the PCR reaction without further purification. This simple method does not require laboratory equipment and can be easily implemented with inexpensive laboratory supplies. Here we describe a protocol for highly sensitive detection and quantitation of HIV-1 proviral DNA from 100 &#181;l whole blood as a model for early infant diagnosis of HIV that could readily be adapted to other genetic targets.

We describe here a simple and rapid paper-based DNA extraction method of HIV proviral DNA from whole blood detected by quantitative PCR. This protocol can be extended for use in detecting other genetic markers or using alternative amplification methods.

FINA, filtration isolation of nucleic acids, is a novel extraction method which utilizes vertical filtration via a separation membrane and absorbent pad ...