Name: localization of sumo-modified proteins using fluorescent sumo-trapping proteins
Uploaded: 2019-04-27T15:00:00
Description: Watch this Scientific Journal Video about Localization of SUMO-modified Proteins Using Fluorescent Sumo-trapping Proteins at JoVE.com

We would like to thank all members of the Kerscher lab for their support, Nathalie Nguyen for critical reading of the manuscript, and Lidia Epp for sequencing. This work has been supported by the Commonwealth Research Commercialization fund MF16-034-LS to OK. Research support for W&#38;M students was provided by the Bailey-Huston Research fund, and Charles Center Honors Fellowships to RY and CH.

1. SUMO detection in fixed tissue culture cells using recombinant KmUTAG-FL SUMO-trapping protein
<ol>
	<li>Grow tissue culture cells of choice on 22 mm round cover slips in 6-well TC plates until 70%&#8211;80% confluent. Perform steps 1.2&#8211;1.8 in the 6-well plate.</li>
	<li>Wash cells briefly with 1 mL of DPBS (Dulbecco&#39;s phosphate-buffered saline)</li>
	<li>For fixation, prepare a fresh solution of 4% Paraformaldehyde (PFA) solution (diluted in DPBS). To fix cells, add 2 mL 4% PFA in DPBS to each well. Incub...

<ol>
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T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=SUMO:+a+history+of+modification.">SUMO: a history of modification.</a> Molecular Cell. 18 (1), 1-12 (2005).</li><li>Fu, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Disruption+of+SUMO-specific+protease+2+induces+mitochondria+mediated+neurodegeneration.">Disruption of SUMO-specific protease 2 induces mitochondria mediated neurodegeneration.</a> PLoS Genetics. 10 (10), e1004579-e1004579 (2014).</li><li>Zhang, H., Kuai, X., Ji, Z., Li, Z., Shi, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Over-expression+of+small+ubiquitin-related+modifier-1+and+sumoylated+p53+in+colon+cancer.">Over-expression of small ubiquitin-related modifier-1 and sumoylated p53 in colon cancer.</a> Cell biochemistry and biophysics. 67 (3), 1081-1087 (2013).</li><li>Wang, Q., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=SUMO-specific+protease+1+promotes+prostate+cancer+progression+and+metastasis.">SUMO-specific protease 1 promotes prostate cancer progression and metastasis.</a> Oncogene. 32 (19), 2493-2498 (2013).</li><li>Karami, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Novel+SUMO-Protease+SENP7S+Regulates+&#946;-catenin+Signaling+and+Mammary+Epithelial+Cell+Transformation.">Novel SUMO-Protease SENP7S Regulates &#946;-catenin Signaling and Mammary Epithelial Cell Transformation.</a> Scientific Reports. 7 (1), 46477 (2017).</li><li>Pelisch, F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+SUMO-Dependent+Protein+Network+Regulates+Chromosome+Congression+during+Oocyte+Meiosis.">A SUMO-Dependent Protein Network Regulates Chromosome Congression during Oocyte Meiosis.</a> Molecular Cell. 65 (1), 66-77 (2017).</li><li>Zhang, X. D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=SUMO-2/3+modification+and+binding+regulate+the+association+of+CENP-E+with+kinetochores+and+progression+through+mitosis.">SUMO-2/3 modification and binding regulate the association of CENP-E with kinetochores and progression through mitosis.</a> Molecular Cell. 29 (6), 729-741 (2008).</li><li>Baker, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reproducibility+crisis:+Blame+it+on+the+antibodies.">Reproducibility crisis: Blame it on the antibodies.</a> Nature News. 521 (7552), 274-276 (2015).</li><li>Wang, Z., Prelich, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quality+control+of+a+transcriptional+regulator+by+SUMO-targeted+degradation.">Quality control of a transcriptional regulator by SUMO-targeted degradation.</a> Molecular and Cellular Biology. 29 (7), 1694-1706 (2009).</li><li>Li, S. J., Hochstrasser, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+new+protease+required+for+cell-cycle+progression+in+yeast.">A new protease required for cell-cycle progression in yeast.</a> Nature. 398 (6724), 246-251 (1999).</li><li>Peek, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=SUMO+targeting+of+a+stress-tolerant+Ulp1+SUMO+protease.">SUMO targeting of a stress-tolerant Ulp1 SUMO protease.</a> PLoS ONE. 13 (1), e0191391 (2018).</li><li>Edgar, L. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chapter+13+Blastomere+Culture+and+Analysis.">Chapter 13 Blastomere Culture and Analysis.</a> Methods in Cell Biology. 48, 303-321 (1995).</li><li>Pelisch, F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dynamic+SUMO+modification+regulates+mitotic+chromosome+assembly+and+cell+cycle+progression+in+Caenorhabditis+elegans.">Dynamic SUMO modification regulates mitotic chromosome assembly and cell cycle progression in Caenorhabditis elegans.</a> Nature Communications. 5 (1), 769 (2014).</li><li>Dillingham, M. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fluorescent+single-stranded+DNA+binding+protein+as+a+probe+for+sensitive,+real-time+assays+of+helicase+activity.">Fluorescent single-stranded DNA binding protein as a probe for sensitive, real-time assays of helicase activity.</a> Biophysical Journal. 95 (7), 3330-3339 (2008).</li><li>Ruckman, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=2'-Fluoropyrimidine+RNA-based+aptamers+to+the+165-amino+acid+form+of+vascular+endothelial+growth+factor+(VEGF165).+Inhibition+of+receptor+binding+and+VEGF-induced+vascular+permeability+through+interactions+requiring+the+exon+7-encoded+domain.">2'-Fluoropyrimidine RNA-based aptamers to the 165-amino acid form of vascular endothelial growth factor (VEGF165). Inhibition of receptor binding and VEGF-induced vascular permeability through interactions requiring the exon 7-encoded domain.</a> The Journal of Biological Chemistry. 273 (32), 20556-20567 (1998).</li><li>Hughes, D. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Generation+of+specific+inhibitors+of+SUMO-1-+and+SUMO-2/3-mediated+protein-protein+interactions+using+Affimer+(Adhiron)+technology.">Generation of specific inhibitors of SUMO-1- and SUMO-2/3-mediated protein-protein interactions using Affimer (Adhiron) technology.</a> Science Signaling. 10 (505), eaaj2005 (2017).</li><li>Lopata, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Affimer+proteins+for+F-actin:+novel+affinity+reagents+that+label+F-actin+in+live+and+fixed+cells.">Affimer proteins for F-actin: novel affinity reagents that label F-actin in live and fixed cells.</a> Scientific Reports. 8 (1), 6572 (2018).</li><li>Gilbreth, R. N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isoform-specific+monobody+inhibitors+of+small+ubiquitin-related+modifiers+engineered+using+structure-guided+library+design.">Isoform-specific monobody inhibitors of small ubiquitin-related modifiers engineered using structure-guided library design.</a> Proceedings of the National Academy of Sciences of the United States of America. 108 (19), 7751-7756 (2011).</li><li>Berndt, A., Wilkinson, K. A., Heimann, M. J., Bishop, P., Henley, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vivo+characterization+of+the+properties+of+SUMO1-specific+monobodies.">In vivo characterization of the properties of SUMO1-specific monobodies.</a> Biochemical Journal. 456 (3), 385-395 (2013).</li></ol>

Here we introduce the use of kmUTAG-fl, a recombinant protein, for functional studies of SUMO in fixed mammalian cells and dissected nematode gonads. KmUTAG-fl is a stress-tolerant pan-SUMO specific reagent that recognizes and traps native SUMO-conjugated proteins and SUMO chains. Since SUMO&#39;s tertiary structure is highly conserved it is very likely that SUMO variants from additional model and non-model systems can be analyzed with the kmUTAG-fl reagent. As such, KmUTAG-fl may represent a useful alternative or second...

The purpose of this method is to facilitate the study and analysis of SUMO-conjugated proteins using the recombinant SUMO-trapping UTAG (Ulp domain Tag) protein. As detailed below, UTAG can be used in lieu of other reagents and approaches to purify, detect, and visualize SUMO-modified proteins. Depending on growth conditions, cells may contain hundreds or thousands of proteins that are modified with SUMO or SUMO chains (for review see Kerscher et al. 20061 and Kerscher 20162). This represents a considerable difficulty for the functional analyses of specific SUMO-modified proteins, especially since only a fraction of a particular sumoylation target is actually modified3. In addition to their roles in essential cellular processes such as transcriptional regulation, protein homeostasis, the response to cellular stress, and chromatin remodeling during mitosis and meiosis; it has now become sufficiently clear that SUMO, SUMO-modified proteins, and SUMO pathway components also have potential as biomarkers for pathologies such as cancer and neurodegenerative disorders4,5,6,7. This underscores the need for robust, reliable, and readily available tools and innovative approaches for the detection and functional analysis of SUMO-modified proteins in a variety of cells and samples.
In many systems, SUMO-specific antibodies are the reagents of choice for the detection, isolation and functional analyses of SUMO-modified proteins8,9. However, some commercially available SUMO-specific antibodies are expensive, limited in quantity or availability, prone to exhibit wildly variable affinities and cross-reactivity, and in some instances lack reproducibility10. One alternative approach is the expression of epitope-tagged SUMO in transformed cells and organisms, but linking epitope tags to SUMO may artificially lower its conjugation to protein targets11. Additionally, epitopes are not useful when untransformed cells or tissues are evaluated.
Ulp1 is a conserved SUMO protease from S. cerevisiae that both processes the SUMO precursor and desumoylates SUMO-conjugated proteins12. We developed the UTAG reagent based on the serendipitous observation that a mutation of the catalytic Cysteine (C580S) in Ulp1&#39;s SUMO processing Ulp domain (UD) not only prevents SUMO cleavage but also traps SUMO-conjugated proteins with high avidity12. For simplicity, we referred to this carboxy-terminal SUMO-trapping Ulp1(C580S) fragment as UTAG (short for UD TAG). UTAG is a recombinant pan-SUMO trapping protein that represents a useful alternative to anti-SUMO antibodies used for the isolation and detection of SUMO-modified proteins. Importantly, it specifically recognizes natively-folded, conjugated SUMO and not just one or several epitopes on SUMO. To improve both the protein stability and SUMO binding strength of UTAG, we generated a variant of UTAG from the stress-tolerant yeast Kluyveromyces marxianus (Km). KmUTAG tightly binds SUMO-conjugates with nanomolar affinity13. Additionally, kmUTAG is resistant to elevated temperatures (42 &#176;C), reducing agents (5 mM TCEP - Tris(2-carboxyethyl)phosphine hydrochloride), denaturants (up to 2 M Urea), oxidizing agents (0.6% hydrogen peroxide), and non-ionic detergents. This stress tolerance is beneficial during harsh purification condition and prolonged incubation times, ensuring its stability and SUMO-trapping activity. Not surprisingly, however, KmUTAG&#39;s SUMO-trapping activity is incompatible with cysteine-modifying reagents, ionic detergents and fully denatured protein extracts. The remarkable affinity and properties of KmUTAG indicate that this reagent may become part of the standard repertoire for the study of sumoylated proteins in multiple species.
Here we provide a simple method to detect SUMO-modified proteins in mammalian cells and nematodes using a recombinant fluorescent mCherry-KmUTAG fusion protein (kmUTAG-fl).

<table>
	<tbody>
		<tr>
			<td>16% Paraformaldehyde (formaldehyde) aqueous solution</td>
			<td>Electron Microscopy Sciences</td>
			<td>30525-89-4</td>
			<td></td>
		</tr>
		<tr>
			<td>6-Well Cell Culture Plates</td>
			<td>Genesee Scientific/Olympus Plastics</td>
			<td>25-105</td>
			<td></td>
		</tr>
		<tr>
			<td>Alexa Fluor 488 AffiniPure Goat Anti-Mouse IgG (H+L)</td>
			<td>Jackson ImmunoResearch</td>
			<td>115-545-003</td>
			<td>Used as a secondary antibody for mouse monoclonal antibody</td>
		</tr>
		<tr>
			<td>DPBS, no calcium, no magnesium</td>
			<td>Fisher Scientific</td>
			<td>Gibco 14190144</td>
			<td></td>
		</tr>
		<tr>
			<td>Dylight 488 conjugated AffiniPure Goat Anti-Moue IgG (H+L)</td>
			<td>Jackson ImmunoResearch</td>
			<td>115-485-146</td>
			<td>Used as a secondary antibody for mouse monoclonal antibody</td>
		</tr>
		<tr>
			<td>Fisherbrand Coverglass for Growth Cover Glasses</td>
			<td>Fisherbrand</td>
			<td>12545101</td>
			<td></td>
		</tr>
		<tr>
			<td>FLUORO-GEL II with DAPI</td>
			<td>Electron Microscopy Sciences</td>
			<td>50-246-93)</td>
			<td>Mounting media in step 1.11</td>
		</tr>
		<tr>
			<td>FLUORO-GEL with DABCO</td>
			<td>Electron Microscopy Sciences</td>
			<td>17985-02</td>
			<td>With DAPI added to 1 &#181;g/mL; mounting media in step 2.2.5</td>
		</tr>
		<tr>
			<td>Glycine-HCl</td>
			<td>Fisher BioReagents</td>
			<td>BP3815</td>
			<td></td>
		</tr>
		<tr>
			<td>Glycine-HCl</td>
			<td>ACROS Organics</td>
			<td>6000-43-7</td>
			<td></td>
		</tr>
		<tr>
			<td>KmUTAG-fl</td>
			<td>Kerafast</td>
			<td></td>
			<td>KmUTAG reagents are available on Kerafast.com</td>
		</tr>
		<tr>
			<td>Oneblock Western-CL blocking buffer</td>
			<td>Prometheus</td>
			<td>20-313</td>
			<td></td>
		</tr>
		<tr>
			<td>PBS, Phosphate Buffered Saline, 10X Solution</td>
			<td>Fisher BioReagents</td>
			<td>BP3994</td>
			<td></td>
		</tr>
		<tr>
			<td>PNT2 cell line</td>
			<td>Sigma-Aldrich</td>
			<td>95012613</td>
			<td>Normal prostate epithelium immortalized with SV40.</td>
		</tr>
		<tr>
			<td>pSPOT1</td>
			<td>(ChromoTek GmbH)</td>
			<td>ev-1</td>
			<td>https://www.chromotek.com/fileadmin/user_upload/pdfs/Datasheets/pSpot1_v1.pdf</td>
		</tr>
		<tr>
			<td>SUMO 6F2</td>
			<td>DSHB</td>
			<td>SUMO 6F2</td>
			<td>SUMO 6F2 was deposited to the DSHB by Pelisch, F. / Hay, R.T. (DSHB Hybridoma Product SUMO 6F2)</td>
		</tr>
		<tr>
			<td>SUMO protease buffer [10x]</td>
			<td></td>
			<td></td>
			<td>500 mM Tris-HCl, pH 8.0, 2% NP-40, 1.5 M NaCl</td>
		</tr>
		<tr>
			<td>SUMO-2 Antibody 8A2</td>
			<td>DSHB</td>
			<td>SUMO-2 8A2</td>
			<td>SUMO-2 8A2 was deposited to the DSHB by Matunis, M. (DSHB Hybridoma Product SUMO-2 8A2)</td>
		</tr>
		<tr>
			<td>TCEP-HCL</td>
			<td>GoldBio</td>
			<td>51805-45-9</td>
			<td>Used as a reducing agent at a concentration of 5mM</td>
		</tr>
		<tr>
			<td>Triton X-100</td>
			<td>Fisher BioReagents</td>
			<td>9002-93-1</td>
			<td>Used for permeablization at 0.1% in DPBS/PBS(for worms)</td>
		</tr>
	</tbody>
</table>

localization of sumo-modified proteins using fluorescent sumo-trapping proteins

Here we are presenting a novel method to study the sumoylation of proteins and their sub-cellular localization in mammalian cells and nematode oocytes. This method utilizes a recombinant modified SUMO-trapping protein fragment, kmUTAG, derived from the Ulp1 SUMO protease of the stress-tolerant budding yeast Kluyveromyces marxianus. We have adapted the properties of the kmUTAG for the purpose of studying sumoylation in a variety of model systems without the use of antibodies. For the study of SUMO, KmUTAG has several advantages when compared to antibody-based approaches. This stress-tolerant SUMO-trapping reagent is produced recombinantly, it recognizes native SUMO isoforms from many species, and unlike commercially available antibodies it shows reduced affinity for free, unconjugated SUMO. Representative results shown here include the localization of SUMO conjugates in mammalian tissue culture cells and nematode oocytes.

KmUTAG-fl is a recombinant, mCherry-tagged SUMO-trapping protein. To produce kmUTAG-fl, we cloned a codon-optimized mCherry-kmUTAG into the pSPOT1 bacterial overexpression plasmid (Figure 1). After induction, the kmUTAG-fl protein was purified on Spot-TRAP, eluted, and frozen until further use. To ensure the SUMO-trapping activity of KmUTAG-fl, we confirmed binding to SUMO1-conjugated beads and precipitation of a SUMO-CAT fusion protein (data not shown, but s...

Watch this Scientific Journal Video about Localization of SUMO-modified Proteins Using Fluorescent Sumo-trapping Proteins at JoVE.com

Localization of SUMO-modified Proteins Using Fluorescent Sumo-trapping Proteins

SUMO is an essential and highly conserved, small ubiquitin-like modifier protein. In this protocol we are describing the use of a stress-tolerant recombinant SUMO-trapping protein (kmUTAG) to visualize native, untagged SUMO conjugates and their localization in a variety of cell types.

Here we are presenting a novel method to study the sumoylation of proteins and their sub-cellular localization in mammalian cells and nematode oocytes. ...

The significance of this protocol is the use of a novel fluorescent SUMO-trapping UTAG protein for the detection of the protein modifier SUMO in various eukaryotic cells. The main advantage of this technique is a straightforward protocol for the antibody-free detection of SUMO in a variety of cells, including mammalian tissue culture and nematode gonads. SUMO plays important roles in cancer and neurodegenerative disorders, and this underscores the need for robust and reliable tools for the detection and functional analysis of SUMO-modified proteins.Because SUMO is highly conserved, the fluorescent SUMO-trapping UTAG protein can be used to label conjugated SUMO in many different organisms. This video demonstrates its use in mammalian cells. In addition, the full text describes its use in nematode oocytes.The visual demonstration of this technique provides critical hints for the treatment of cells before staining and SUMO detection. To begin, grow tissue culture cells of choice on 22-millimeter round cover slips in six-well TC plates until 70 to 80%confluent. Wash the cells briefly with one milliliter of DPBS.To fix the cells, add two milliliters of fresh 4%PFA and DPBS to each well. Incubate the cells for 20 minutes at room temperature. Wash the fixed cells three times for five minutes in one milliliter of DPBS while nutating the plate.To permeabilize the cells, incubate for 15 minutes with 1%Triton X-100 in DPBS. Wash the cells again, as before. Incubate the cells with 500 microliters of 1 molar glycine HCL pH 2 for 10 seconds.Then neutralize the pH immediately with 500 microliters of 10X SUMO Protease buffer, or SPB. After washing the cells as before, remove the cover slips from the well and place them in a humidity chamber. For UTAG-FL staining only, mix one microgram of UTAG-FL with 100 microliters of 1X SPB containing five millimolar TCEP in a tube.Then, pipette the mix onto the cells on the cover slip and incubate at room temperature for one hour in the humidity chamber. To wash the cover slips, pipette 200 microliters of DPBS on each cover slip and leave in place for 10 minutes. Repeat the wash two more times.Remove the cover slips from the last wash and invert onto a pre-cleaned microscopy slide with a drop of mounting medium. Store the samples overnight in a 20 degree Celsius freezer before viewing under the microscope. Visualize the cells using the appropriate filter sets for DAPI and Texas Red.Please see the full text for a protocol on how to label SUMO and fixed nematode gonads. While labeling mammalian cells is pretty straightforward, labeling nematode oocytes requires prior training in gonad dissections. KmUTAG-FL incubated with fixed PMT2 cells showed a distinct nuclear staining.Both diffuse nuclear staining and distinct nuclear foci were visible. Nuclear localization was confirmed using co-staining with DAPI. Consistent with the SUMO trapping activity of KmUTAG-FL, the nuclear localization pattern was reminiscent of SUMO23 staining.Co-staining with anti-SUMO23 8A2 antibody confirmed the co-localization of KmUTAG-FL with the SUMO23 signal. This validates the efficacy of KmUTAG-FL to detect SUMO23 in mammalian cells. Isolated gonads from oocyte-producing adult hermaphrodite c.elegans nematodes were labeled with anti-SUMO antibody. Consistent with previous reports, anti-SUMO antibody initially localized to the nuclear plasm of late myotic prophase oocytes. It then redistributed to the central ring complex of the paired homologs as the nuclear envelope broke down and the chromosomes congressed towards the metaphase plate.In parallel preparations, gonads labeled with KmUTAG-FL revealed similar patterns. KmUTAG-FL shifted from labeling the nucleoplasm to concentrating on the ring complex as oocytes began and completed the process of nuclear envelope breakdown. These results validate KmUTAG-FL as a useful tool for the analysis of myosis and SUMO-related processes in c.elegans and possibly other nematodes. While performing fixation, it is critical to use fresh paraformaldehyde and a short fixation time to keep SUMO natively folded so that it can be recognized by the KmUTAG. Since SUMO's tertiary structure is highly conserved, it is very likely that SUMO variants from additional model and non-model systems can be analyzed with the KmUTAG-FL reagent.Currently, we are using this novel fluorescent SUMO-trapping UTAG protein to study the function of SUMO during cellular stress. Finally, please note that all steps using the fixative paraformaldehyde should be performed in a laboratory safety hood and this reagent must be disposed of properly.

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