We thank current and former members of the Rubenstein lab for providing a supportive and enthusiastic research environment. We thank Ryan T. Gibson for assistance in protocol optimization. We thank Mark Hochstrasser (Yale University) and Dieter Wolf (Universit&#228;t Stuttgart) for yeast strains and plasmids. We thank our anonymous reviewers for their help in improving the clarity and utility of this manuscript. This work was supported by a research award from the Ball State University chapter of Sigma Xi to S.G.W., a National Institutes of Health grant (R15 GM111713) to E.M.R., a Ball State University ASPiRE research award to E.M.R, and funds from the Ball State University Provost&#8217;s Office and Department of Biology.

1. Yeast Growth Assay to Identify Candidate Mutants Defective in Protein Degradation
<ol>
	<li>Transform wild-type and mutant yeast cells with a plasmid encoding an unstable protein fused, in frame, to a reporter metabolic enzyme.</li>
	<li>Inoculate transformants in 5 ml of synthetic defined (SD) minimal medium that is selective for cells harboring plasmid molecules. Incubate overnight at 30 &#176;C, rotating.</li>
	<li>Measure the optical density at 600 nm (OD600) of each overnight culture. 
	NOTE: Following overnight incubation, cells in culture may be in either logarithmic or stationary growth phase but should have reached a minimal OD600 of 0.2. Very slow-growing yeast strains may require incubation times longer than one night, or inoculation of a greater number of cells, as determined empirically.</li>
	<li>Prepare six-fold serial dilutions of transformed yeast cells in a sterile 96-well plate, beginning with cells diluted to an OD600 of 0.2. Place each yeast transformant to be assayed in a different row in the 96-well plate.
	<ol>
		<li>For each transformant, calculate the volume of overnight culture required to dilute cells to an OD600 of 0.2 in a final volume of 200 &#181;l. Add this volume of overnight culture to the corresponding well in Column 1. Add the appropriate amount of sterile water to bring the volume to 200 &#181;l.</li>
		<li>For each row of yeast, add 125 &#181;l of sterile water to the wells in Columns 2, 3, and 4. 
		NOTE: Individually wrapped sterile 96-well plates may be packaged with sterile lids. The lids may be used as reservoirs for the sterile water that is distributed in this step. This allows simultaneous transfer of sterile water to all wells in a given column with a multichannel pipettor.</li>
		<li>Mix the contents of the first column (yeast diluted to an OD600 of 0.2) by pipetting up and down with a multichannel pipettor.</li>
		<li>Transfer 25 &#181;l of yeast from Column 1 to Column 2, using a multichannel pipettor. Mix by pipetting up and down. Transfer 25 &#181;l from Column 2 to Column 3, and 25 &#181;l from Column 3 to Column 4 (mixing well at each step).</li>
	</ol>
	</li>
	<li>Mix each sample with a multichannel pipettor. Proceeding from most dilute to least dilute columns of yeast, pipette 4 &#181;l of each sample onto two plates containing the appropriate selective medium. Use one plate with medium that maintains plasmid selection (this plate serves as a yeast spotting and growth control). Use a second plate with medium that selects for plasmid maintenance and expression of the unstable protein fused to the reporter enzyme. Because yeast settle rapidly, mix cells by pipetting up and down at regular intervals. 
	NOTE: Drier plates will more readily absorb liquid than freshly prepared plates and are therefore recommended for these experiments. Damp plates may be dried by incubation at room temperature in low humidity for 1 &#8211; 2 days or shorter incubations in a laminar flow hood. Plates may dry unevenly if the laminar air flow is parallel to the bench. Use of a template makes it easier to spot yeast cells at regular distances. Two sample templates are provided in Figure 1. These may be printed, cut out, and affixed to the inside of a Petri dish lid.</li>
	<li>Allow plates to dry on the bench top.</li>
	<li>Incubate plates at 30 &#176;C for 2 &#8211; 6 days.</li>
	<li>Photograph each plate after incubation.</li>
</ol>
<img alt="Figure 1" src="/files/ftp_upload/52428/52428fig1large.jpg" width="650" /> 
Figure 1. Templates for spotting yeast cells onto 100-mm agar plates. These templates may be used to facilitate spotting yeast at regular distances with a multichannel pipettor. Templates may be printed, cut out, and affixed to the inside of a Petri dish lid. Place Petri dish with growth medium inside lid with template affixed. Templates are marked with a notch to track orientation. It is recommended that plates used in growth assays be similarly marked with a notch to track orientation. Templates for spotting four (A) or five (B) serial dilutions of yeast cells are provided. <a href="https://www.jove.com/files/ftp_upload/52428/150126 Fig 1.pdf" target="_blank">Please click here to view a printable version of this figure with 100-mm templates.</a>
2. Biochemical Confirmation of Yeast Growth Assay
<ol>
	<li>Growth of Yeast Cells and Post-Alkaline Protein Extraction (modified from 31)
	<ol>
		<li>Transform wild-type and mutant yeast cells with a plasmid encoding the unstable protein.</li>
		<li>Inoculate transformants in 5 ml of SD medium that is selective for cells harboring plasmid molecules. Incubate overnight at 30 &#176;C, rotating.</li>
		<li>Measure the OD600 of each overnight culture. 
		NOTE: Following overnight incubation, cells may be in either logarithmic or stationary growth phase but should have reached an OD600 that will permit dilution to an OD600 of 0.2 in 10 ml fresh selective medium (step 2.1.4). Very slow-growing yeast strains may require incubation times longer than one night, or inoculation of a greater number of cells, as determined empirically.</li>
		<li>Dilute yeast cells to an OD600 of 0.2 in 10 ml fresh selective medium.</li>
		<li>Continue to incubate cells at 30 &#176;C, rotating or shaking, until cultures reach an OD600 between 0.8 and 1.2 (i.e. are in mid-logarithmic growth). 
		NOTE: If the unstable protein of interest is under the control of a regulatable promoter, the optimal timing of induction of protein expression and cell harvest may vary according to previous studies or empirical observations.</li>
		<li>Collect 2.5 OD600 units of culture in a 15-ml conical tube by centrifugation at 5,000 x g for 5 min at room temperature. Remove supernatant by pipetting or aspiration. 
		NOTE: One OD600 unit is defined as the amount of yeast present in 1 ml of culture at OD600 of 1.0. The volume of culture (in ml) required to harvest 2.5 OD600 units (V) can be determined using the following equation: V = 2.5 OD600 units / Measured OD600</li>
		<li>Resuspend cells in 1 ml distilled water. Transfer suspended cells to a microcentrifuge tube.</li>
		<li>Pellet cells by centrifugation at 6,500 x g for 30 sec at room temperature. Remove supernatant by pipetting or aspiration.</li>
		<li>Resuspend cells in 100 &#181;l distilled water by pipetting up and down or vortexing, and add 100 &#181;l 0.2 M NaOH. Mix by pipetting up and down. Incubate samples for 5 min at room temperature.</li>
		<li>Pellet cells (most of which have not yet released proteins and are still viable) by centrifugation at 18,000 x g for 5 min. Remove supernatant by pipetting or aspiration.</li>
		<li>Resuspend pellet in 50 &#8211; 100 &#181;l 1x Laemmli sample buffer, which will lyse cells, by pipetting up and down or vortexing. 
		NOTE: Removal of the alkaline supernatant following centrifugation and subsequent resuspension of cells in Laemmli sample buffer extracts proteins at a pH compatible with sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) using a Tris-glycine running buffer system and western blotting.</li>
		<li>To fully denature proteins, incubate lysates at 95 &#176;C for 5 min. 
		NOTE: Aggregation-prone proteins (e.g. proteins with several transmembrane segments) may become insoluble when incubated at 95 &#176;C. Therefore, lysates should be incubated at lower temperatures (e.g. 37 &#176;C &#8211; 70 &#176;C) for 10 &#8211; 30 min, as empirically determined, for the analysis of such proteins.</li>
		<li>Cool lysates by placing on ice for 5 min.</li>
		<li>Centrifuge lysates at 18,000 x g for 1 min at room temperature to pellet insoluble material. Separate the supernatant (solubilized extracted protein) by SDS-PAGE prior to subsequent western blot analysis (section 2.2). Alternatively, store lysates at -20 &#176;C.</li>
	</ol>
	</li>
	<li>Representative Western Blotting Protocol
	<ol>
		<li>Load empirically determined volume of lysates in an SDS-PAGE gel.</li>
		<li>Run gel at 200 V until dye front has reached the bottom of the gel.</li>
		<li>Transfer proteins from gel to polyvinylidene fluoride (PVDF) membrane by wet transfer at 20 V for 60 &#8211; 90 min at 4 &#176;C.</li>
		<li>Block membrane by incubating in 5% skim milk in Tris-Buffered Saline (TBS), rocking, for 1 hr at room temperature or overnight at 4 &#176;C.</li>
		<li>Decant blocking solution.</li>
		<li>Incubate membrane with primary antibody specific for protein of interest (or epitope tag thereof) in 1% skim milk in TBS with 0.1% Tween-20 (TBS/T) for 1 hr at room temperature, rocking.</li>
		<li>Decant antibody solution, and wash membrane 3 x 5 min with TBS/T at room temperature, rocking.</li>
		<li>Incubate membrane with appropriate fluorophore-conjugated secondary antibody in 1% skim milk in TBS/T for 1 hr at room temperature, rocking. 
		NOTE: Because fluorophores are light-sensitive, dilutions of fluorophore-conjugated antibodies should be prepared in the dark. Additionally, incubation of membranes in the presence of fluorophore-conjugated antibodies should occur in lightproof containers. This can be accomplished by wrapping incubation trays in aluminum foil.</li>
		<li>Decant antibody solution, and wash membrane 3 x 5 min with TBS/T at room temperature, rocking.</li>
		<li>Acquire image of membrane using Li-Cor Odyssey CLx and Image Studio software (or comparable imaging equipment and software), according to manufacturer recommendations.</li>
		<li>After imaging membrane, incubate the membrane with a primary antibody specific for a loading control protein in 1% skim milk in TBS/T for 1 hr at room temperature, rocking.</li>
		<li>Decant antibody solution, and wash membrane 3 x 5 min with TBS/T at room temperature, rocking.</li>
		<li>Incubate membrane with appropriate fluorophore-conjugated secondary antibody in 1% skim milk in TBS/T for 1 hr at room temperature, rocking.</li>
		<li>Decant antibody solution, and wash membrane 3 x 5 min with TBS/T at room temperature, rocking.</li>
		<li>Acquire image of membrane using Li-Cor Odyssey CLx and Image Studio software (or comparable imaging equipment and software), according to manufacturer recommendations.</li>
	</ol>
	</li>
</ol>

The authors have nothing to disclose.

The methodology presented here allows for the rapid determination and biochemical confirmation of genetic requirements for protein degradation in yeast cells. These experiments highlight the utility and power of yeast as a model eukaryotic organism (several excellent reviews of yeast biology and compilations of protocols for handling, storing, and manipulating yeast cells (e.g. 41-44) are available for investigators new to the organism). The techniques can readily be applied to investigate the degrada...

Selective protein degradation is essential for eukaryotic life, and altered protein degradation contributes to a number of medical conditions, including several types of cancer, neurodegenerative disease, cardiovascular disease, and cystic fibrosis1-5. The ubiquitin-proteasome system (UPS), which catalyzes selective protein degradation, is an emerging therapeutic target for these conditions6-10. Ubiquitin ligases covalently attach polymers of the 76-amino acid ubiquitin to proteins11. Proteins that have been marked with polyubiquitin chains are recognized and proteolyzed by the ~2.5 megadalton 26S proteasome12. Studies initiated in the model eukaryotic organism Saccharomyces cerevisiae (budding yeast) have been foundational in the elucidation of protein degradation mechanisms in eukaryotic cells. The first demonstrated physiological substrate of the UPS was the yeast transcriptional repressor MAT&#945;213,14, and many highly conserved components of the UPS were first identified or characterized in yeast (e.g. 15-26). Discoveries made in this versatile and genetically tractable model organism are likely to continue to provide important insights into conserved mechanisms of ubiquitin-mediated degradation.
Recognition and degradation of most UPS substrates require the concerted action of multiple proteins. Therefore, an important goal in characterizing the regulated degradation of a given unstable protein is to determine the genetic requirements for proteolysis. Classical approaches (e.g. pulse-chase and cycloheximide-chase experiments27) for monitoring protein degradation in mammalian or yeast cells are laborious and time-consuming. While these types of methodology provide highly sensitive means for detecting protein degradation, they are not suitable for rapid analysis of protein degradation or large-scale screening for mutations that prevent protein degradation. Here, a yeast growth-based assay for the rapid identification of genetic requirements for the degradation of unstable proteins is presented.
In the yeast growth-based method for analyzing protein degradation, an unstable protein of interest (or degradation signal) is fused, in frame, to a protein that is required for yeast growth under specific circumstances. The result is an artificial substrate that may serve as a powerful tool to determine the genetic requirements of protein degradation of the unstable protein of interest. Conveniently, most commonly used laboratory yeast strains harbor a panel of mutations in genes encoding metabolic enzymes involved in the biosynthesis of particular amino acids or nitrogenous bases (e.g. 20,28-30). These enzymes are essential for cellular proliferation in the absence of exogenously provided metabolites in whose synthesis the enzymes participate. Such metabolic enzymes may thus function as growth-based reporters for the degradation of unstable proteins to which they are fused. The genetic requirements for protein degradation can be readily elucidated, since mutations that prevent proteolysis will allow cells harboring the degradation reporter to grow under selective conditions.
A growth advantage is an indirect indication that a particular mutation increases the abundance of the protein of interest. However, direct biochemical analysis is required to confirm that a mutation permits growth through increased protein levels rather than via indirect or artifactual causes. The effect of a mutation on protein abundance may be confirmed by western blot analysis of steady-state protein levels in cells that do and do not harbor the particular mutation. A method for the rapid and efficient extraction of yeast proteins (sequential incubation of yeast cells with sodium hydroxide and sample buffer) in a form suitable for analysis by western blotting is also presented31. Together, these experiments facilitate the rapid identification of candidate regulators of protein degradation.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>Desired yeast strains, plasmids, standard medium and buffer components</td>
			<td></td>
			<td></td>
			<td>Yeast strains with desired mutations may be generated in the investigator&#39;s laboratory. Wild-type yeast and a variety of mutants are also commercially available (e.g. from GE Healthcare). Plasmids encoding fusion proteins may be generated in the investigator&#39;s laboratory.</td>
		</tr>
		<tr>
			<td>3-amino-1H-1,2,4-triazole</td>
			<td>Fisher Scientific</td>
			<td>AC264571000</td>
			<td>Competitive inhibitor of His3 enzyme. May be included in medium to increase stringency of growth assay using His3 reporter constructs</td>
		</tr>
		<tr>
			<td>Endoglycosidase H (recombinant form from Streptomyces plicatus)</td>
			<td>Roche</td>
			<td>11088726001</td>
			<td>May be used to assess N-glycosylation of proteins; compatible with SDS and beta-mercaptoethanol concentrations found in 1X Laemmli sample buffer</td>
		</tr>
		<tr>
			<td>Disposable borosilicate glass tubes</td>
			<td>Fisher Scientific</td>
			<td>14-961-32</td>
			<td>Available from a variety of manufacturers</td>
		</tr>
		<tr>
			<td>Temperature-regulated incubator (e.g. Heratherm Incubator Model IMH180)</td>
			<td>Dot Scientific</td>
			<td>51028068</td>
			<td>Available from a variety of manufacturers</td>
		</tr>
		<tr>
			<td>New Brunswick Interchangeable Drum for 18 mm tubes (tube roller)</td>
			<td>New Brunswick</td>
			<td>M1053-0450</td>
			<td>Tube roller is recommended to maintain overnight yeast starter cultures of yeast cells in suspension. A platform shaker or tube roller may be used to maintain larger cultures in suspension.</td>
		</tr>
		<tr>
			<td>New Brunswick TC-7 Roller Drum 120V 50/60 H</td>
			<td>New Brunswick</td>
			<td>M1053-4004</td>
			<td>For use with tube roller</td>
		</tr>
		<tr>
			<td>SmartSpec Plus Spectrophotometer</td>
			<td>Bio-Rad</td>
			<td>170-2525</td>
			<td>Available from a variety of manufacturers</td>
		</tr>
		<tr>
			<td>Sterile 96-well flat bottom microtest plates with lid individually wrapped</td>
			<td>Sarstedt</td>
			<td>82.1581.001</td>
			<td>Available from a variety of manufacturers</td>
		</tr>
		<tr>
			<td>Pipetman Neo P8x200N, 20-200 &#956;l</td>
			<td>Gilson</td>
			<td>F14403</td>
			<td>Single-channel and multichannel pipettors are used at various stages of the protocol. While multichannel pipettors reduce the pipetting burden at several steps, single-channel pipettors may be used throughout the entire protocol. Available from a variety of manufacturers</td>
		</tr>
		<tr>
			<td>Pipetman Neo P8x20N, 2-20 &#956;l</td>
			<td>Gilson</td>
			<td>F14401</td>
			<td>Available from a variety of manufacturers</td>
		</tr>
		<tr>
			<td>Plate imaging system (e.g. 
			Gel Doc XR+ System)</td>
			<td>Bio-Rad</td>
			<td>170-8195</td>
			<td>A variety of systems may be used to image plates, including sophisticated imaging systems, computer scanners, and camera phones.</td>
		</tr>
		<tr>
			<td>Centrifuge 5430</td>
			<td>Eppendorf</td>
			<td>5427 000.216&#160;</td>
			<td>Rotor that is sold with unit holds 1.5 and 2.0 mL microcentrifuge tubes. Rotor may be swapped for one that holds 15 ml and 50 ml conical tubes</td>
		</tr>
		<tr>
			<td>Fixed-Angle Rotor F-35-6-30 with Lid and Adapters for Centrifuge Model 5430/R, 15/50 mL Conical Tubes, 6-Place</td>
			<td>Eppendorf</td>
			<td>F-35-6-30</td>
			<td></td>
		</tr>
		<tr>
			<td>15 ml screen printed screw cap tube 17 x 20 mm conical, polypropylene</td>
			<td>Sarstedt</td>
			<td>62.554.205</td>
			<td>Available from a variety of manufacturers</td>
		</tr>
		<tr>
			<td>1.5 ml flex-tube, PCR clean, Natural microcentrifuge tubes</td>
			<td>Eppendorf</td>
			<td>22364120</td>
			<td>Available from a variety of manufacturers</td>
		</tr>
		<tr>
			<td>Analog Dri-Bath Heater</td>
			<td>Fisher Scientific</td>
			<td>1172011AQ</td>
			<td>Boiling water bath with hot plate may also be used to denature proteins</td>
		</tr>
		<tr>
			<td>SDS-PAGE running and transfer apparatuses, power supplies, and imaging equipment or darkrooms for SDS-PAGE and transfer to membrane</td>
			<td></td>
			<td></td>
			<td>Will vary by lab and application</td>
		</tr>
		<tr>
			<td>Western blot imaging system (e.g. Li-Cor Odyssey CLx scanner and Image Studio Software)</td>
			<td>Li-Cor</td>
			<td>9140-01</td>
			<td>Will vary by lab and application</td>
		</tr>
		<tr>
			<td>EMD Millipore Immobilon PVDF Transfer Membranes</td>
			<td>Fisher Scientific</td>
			<td>IPFL00010</td>
			<td>Will vary by lab and application</td>
		</tr>
		<tr>
			<td>Primary antibodies (e.g. Phosphoglycerate Kinase (Pgk1) Monoclonal antibody, mouse (clone 22C5D8))</td>
			<td>Life Technologies</td>
			<td>459250</td>
			<td>Will vary by lab and application</td>
		</tr>
		<tr>
			<td>Secondary antibodies (e.g. Alexa-Fluor 680 Rabbit Anti-Mouse IgG (H+L))</td>
			<td>Life Technologies</td>
			<td>A-21065</td>
			<td>Will vary by lab and application</td>
		</tr>
	</tbody>
</table>

growth-based determination and biochemical confirmation of genetic requirements for protein degradation in saccharomyces cerevisiae

Regulated protein degradation is crucial for virtually every cellular function. Much of what is known about the molecular mechanisms and genetic requirements for eukaryotic protein degradation was initially established in Saccharomyces cerevisiae. Classical analyses of protein degradation have relied on biochemical pulse-chase and cycloheximide-chase methodologies. While these techniques provide sensitive means for observing protein degradation, they are laborious, time-consuming, and low-throughput. These approaches are not amenable to rapid or large-scale screening for mutations that prevent protein degradation. Here, a yeast growth-based assay for the facile identification of genetic requirements for protein degradation is described. In this assay, a reporter enzyme required for growth under specific selective conditions is fused to an unstable protein. Cells lacking the endogenous reporter enzyme but expressing the fusion protein can grow under selective conditions only when the fusion protein is stabilized (i.e. when protein degradation is compromised). In the growth assay described here, serial dilutions of wild-type and mutant yeast cells harboring a plasmid encoding a fusion protein are spotted onto selective and non-selective medium. Growth under selective conditions is consistent with degradation impairment by a given mutation. Increased protein abundance should be biochemically confirmed. A method for the rapid extraction of yeast proteins in a form suitable for electrophoresis and western blotting is also demonstrated. A growth-based readout for protein stability, combined with a simple protocol for protein extraction for biochemical analysis, facilitates rapid identification of genetic requirements for protein degradation. These techniques can be adapted to monitor degradation of a variety of short-lived proteins. In the example presented, the His3 enzyme, which is required for histidine biosynthesis, was fused to Deg1-Sec62. Deg1-Sec62 is targeted for degradation after it aberrantly engages the endoplasmic reticulum translocon. Cells harboring Deg1-Sec62-His3 were able to grow under selective conditions when the protein was stabilized.

To illustrate this methodology, the His3 enzyme has been fused to the carboxy-terminus of the model endoplasmic reticulum (ER)-associated degradation (ERAD) substrate, Deg1-Sec62 (Figure 2A) to create Deg1-Sec62-His3 (Figure 3). Deg1-Sec62 represents a founding member of a novel class of ERAD substrates that are targeted following persistent, aberrant association with the translocon, the channel primarily responsible for moving proteins across the ER membrane<s...

Watch this Scientific Journal Video about Growth-based Determination and Biochemical Confirmation of Genetic Requirements for Protein Degradation in Saccharomyces cerevisiae at JoVE.com

Growth-based Determination and Biochemical Confirmation of Genetic Requirements for Protein Degradation in Saccharomyces cerevisiae

This article describes a yeast growth-based assay for the determination of genetic requirements for protein degradation. It also demonstrates a method for rapid extraction of yeast proteins, suitable for western blotting to biochemically confirm degradation requirements. These techniques can be adapted to monitor degradation of a variety of proteins.

Growth-based Determination and Biochemical Confirmation of Genetic Requirements for Protein Degradation in Saccharomyces cerevisiae

Regulated protein degradation is crucial for virtually every cellular function. Much of what is known about the molecular mechanisms and genetic ...

growth-based-determination-biochemical-confirmation-genetic

Research

JoVE Journal

Biology

9.6K Views.  Ball State University. This article describes a yeast growth-based assay for the determination of genetic requirements for protein degradation. It also demonstrates a method for rapid extraction of yeast proteins, suitable for western blotting to biochemically confirm degradation requirements. These techniques can be adapted to monitor degradation of a variety of proteins.

Video: Growth-based Determination and Biochemical Confirmation of Genetic Requirements for Protein Degradation in Saccharomyces cerevisiae

Dissection of Saccharomyces Cerevisiae Asci

Yeast is a highly tractable model system that is used to study many different cellular processes. The common laboratory strain Saccharomyces cerevisiae exists in either a haploid or diploid state. The ability to combine alleles from two haploids and the ability to introduce modifications to the genome requires the production and dissection of asci. Asci production from haploid cells begins with the mating of two yeast haploid strains with compatible mating types to produce a diploid strain. This can be accomplished in a number of ways either on solid medium or in liquid. It is advantageous to select for the diploids in medium that selectively promotes their growth compared to either of the haploid strains. The diploids are then allowed to sporulate on nutrient-poor medium to form asci, a bundle of four haploid daughter cells resulting from meiotic reproduction of the diploid. A mixture of vegetative cells and asci is then treated with the enzyme zymolyase to digest away the membrane sac surrounding the ascospores of the asci. Using micromanipulation with a microneedle under a dissection microscope one can pick up individual asci and separate and relocate the four ascopores. Dissected asci are grown for several days and tested for the markers or alleles of interest by replica plating onto appropriate selective media.

Dissection of Saccharomyces Cerevisiae Asci

Micromanipulation of yeast cells is needed for meiotic genetic analysis or to select diploid zygotes. These micromanipulations are carried out using the microneedle of a dissection microscope. The microneedle is used to relocate cells and is controlled by a micromanipulator which are available with various degrees of automation.

Yeast is a highly tractable model system that is used to study many different cellular processes. The common laboratory strain Saccharomyces cerevisiae ...

Quantitative Phosphoproteomics in Fatty Acid Stimulated Saccharomyces cerevisiae

This protocol describes the growth and stimulation, with the fatty acid oleate, of isotopically heavy and light S. cerevisiae cells. Cells are ground using a cryolysis procedure in a ball mill grinder and the resulting grindate brought into solution by urea solubilization. This procedure allows for the lysis of the cells in a metabolically inactive state, preserving phosphorylation and preventing reorientation of the phosphoproteome during cell lysis.  Following reduction, alkylation, trypsin digestion of the proteins, the samples are desalted on C18 columns and the sample complexity reduced by fractionation using hydrophilic interaction chromatography (HILIC). HILIC columns preferentially retain hydrophilic molecules which is well suited for phosphoproteomics.  Phosphorylated peptides tend to elute later in the chromatographic profile than the non phosphorylated counterparts. After fractionation, phosphopeptides are enriched using immobilized metal chromatography, which relies on charge-based affinities for phosphopeptide enrichment. At the end of this procedure the samples are ready to be quantitatively analyzed by mass spectrometry.

Quantitative Phosphoproteomics in Fatty Acid Stimulated Saccharomyces cerevisiae

Description of a quantitative phosphorylation procedure using cryolysis, urea solubilziation, HILIC fractionation and IMAC enrichment of phosphorylated peptides.

This protocol describes the growth and stimulation, with the fatty acid oleate, of isotopically heavy and light S. cerevisiae cells. Cells are ground ...

Microarray Analysis for Saccharomyces cerevisiae

In this protocol, gene expression in yeast (Saccharomyces cerevisiae) is changed after exposure to oxidative stress induced by the addition of hydrogen peroxide (H2O2), an oxidizing agent. In the experiment, yeast is grown for 48 hours in 1/2X YPD broth containing 3X glucose. The culture is split into a control and treated group. The experiment culture is treated with 0.5 mM H2O2 in Hanks Buffered Saline (HBSS) for 1 hour. The control culture is treated with HBSS only. Total RNA is extracted from both cultures and is converted to a biotin-labeled cRNA product through a multistep process. The final synthesis product is taken back to the UVM Microarray Core Facility and hybridized to the Affymetrix yeast GeneChips. The resulting gene expression data are uploaded into bioinformatics data analysis software.

Microarray Analysis for Saccharomyces cerevisiae

In this protocol, gene expression in yeast (Saccharomyces cerevisiae) is changed after exposure to oxidative stress induced by the addition of hydrogen peroxide (H2O2), an oxidizing agent.

In this protocol, gene expression in yeast (Saccharomyces cerevisiae) is changed after exposure to oxidative stress induced by the addition of hydrogen ...

A Fluorescence Microscopy Assay for Monitoring Mitophagy in the Yeast Saccharomyces cerevisiae

Autophagy is important for turnover of cellular components under a range of different conditions. It serves an essential homeostatic function as well as a quality control mechanism that can target and selectively degrade cellular material including organelles1-4. For example, damaged or redundant mitochondria (Fig. 1), not disposed of by autophagy, can represent a threat to cellular homeostasis and cell survival. In the yeast, Saccharomyces cerevisiae, nutrient deprivation (e.g., nitrogen starvation) or damage can promote selective turnover of mitochondria by autophagy in a process termed mitophagy 5-9.
We describe a simple fluorescence microscopy approach to assess autophagy. For clarity we restrict our description here to show how the approach can be used to monitor mitophagy in yeast cells. The assay makes use of a fluorescent reporter, Rosella, which is a dual-emission biosensor comprising a relatively pH-stable red fluorescent protein linked to a pH-sensitive green fluorescent protein. The operation of this reporter relies on differences in pH between the vacuole (pH ~ 5.0-5.5) and mitochondria (pH ~ 8.2) in living cells. Under growing conditions, wild type cells exhibit both red and green fluorescence distributed in a manner characteristic of the mitochondria. Fluorescence emission is not associated with the vacuole. When subjected to nitrogen starvation, a condition which induces mitophagy, in addition to red and green fluorescence labeling the mitochondria, cells exhibit the accumulation of red, but not green fluorescence, in the acidic vacuolar lumen representing the delivery of mitochondria to the vacuole. Scoring cells with red, but not green fluorescent vacuoles can be used as a measure of mitophagic activity in cells5,10-12.

A Fluorescence Microscopy Assay for Monitoring Mitophagy in the Yeast Saccharomyces cerevisiae

A robust approach to monitor the delivery of organelles to the acidic lumen of the yeast vacuole for degradation and recycling is described. The method relies on the specific labeling of target organelles with a genetically encoded dual-emission fluorescence pH-biosensor, and visualization of individual cells using fluorescence microscopy.

Autophagy is important for turnover of cellular components under a range of different conditions. It serves an essential homeostatic function as well as a ...

Expression and Purification of the Cystic Fibrosis Transmembrane Conductance Regulator Protein in Saccharomyces cerevisiae

The cystic fibrosis transmembrane conductance regulator (CFTR) is a chloride channel, that when mutated, can give rise to cystic fibrosis in humans.There is therefore considerable interest in this protein, but efforts to study its structure and activity have been hampered by the difficulty of expressing and purifying sufficient amounts of the protein1-3. Like many 'difficult' eukaryotic membrane proteins, expression in a fast-growing organism is desirable, but challenging, and in the yeast S. cerevisiae, so far low amounts were obtained and rapid degradation of the recombinant protein was observed 4-9. Proteins involved in the processing of recombinant CFTR in yeast have been described6-9 .In this report we describe a methodology for expression of CFTR in yeast and its purification in significant amounts. The protocol describes how the earlier proteolysis problems can be overcome and how expression levels of CFTR can be greatly improved by modifying the cell growth conditions and by controlling the induction conditions, in particular the time period prior to cell harvesting. The reagants associated with this protocol (murine CFTR-expressing yeast cells or yeast plasmids) will be distributed via the US Cystic Fibrosis Foundation, which has sponsored the research. An article describing the design and synthesis of the CFTR construct employed in this report will be published separately (Urbatsch, I.; Thibodeau, P. et al., unpublished). In this article we will explain our method beginning with the transformation of the yeast cells with the CFTR construct - containing yeast plasmid (Fig. 1). The construct has a green fluorescent protein (GFP) sequence fused to CFTR at its C-terminus and follows the system developed by Drew et al. (2008)10. The GFP allows the expression and purification of CFTR to be followed relatively easily. The JoVE visualized protocol finishes after the preparation of microsomes from the yeast cells, although we include some suggestions for purification of the protein from the microsomes. Readers may wish to add their own modifications to the microsome purification procedure, dependent on the final experiments to be carried out with the protein and the local equipment available to them. The yeast-expressed CFTR protein can be partially purified using metal ion affinity chromatography, using an intrinsic polyhistidine purification tag. Subsequent size-exclusion chromatography yields a protein that appears to be &gt;90% pure, as judged by SDS-PAGE and Coomassie-staining of the gel.

Expression and Purification of the Cystic Fibrosis Transmembrane Conductance Regulator Protein in Saccharomyces cerevisiae

Attempts to express the cystic fibrosis transmembrane conductance regulator (CFTR) in Saccharomyces cerevisiae have, until now, yielded relatively low amounts of protein. This protocol and the associated reagents distributed via the Cystic Fibrosis Foundation should allow the preparation of milligram amounts of this 'difficult' eukaryotic membrane protein.

The  cystic fibrosis transmembrane conductance regulator (CFTR) is a chloride  channel, that when mutated, can give rise to cystic fibrosis in  ...

Biochemical and High Throughput Microscopic Assessment of Fat Mass in Caenorhabditis Elegans

The nematode C. elegans has emerged as an important model for the study of conserved genetic pathways regulating fat metabolism as it relates to human obesity and its associated pathologies. Several previous methodologies developed for the visualization of C. elegans triglyceride-rich fat stores have proven to be erroneous, highlighting cellular compartments other than lipid droplets. Other methods require specialized equipment, are time-consuming, or yield inconsistent results. We introduce a rapid, reproducible, fixative-based Nile red staining method for the accurate and rapid detection of neutral lipid droplets in C. elegans. A short fixation step in 40% isopropanol makes animals completely permeable to Nile red, which is then used to stain animals. Spectral properties of this lipophilic dye allow it to strongly and selectively fluoresce in the yellow-green spectrum only when in a lipid-rich environment, but not in more polar environments. Thus, lipid droplets can be visualized on a fluorescent microscope equipped with simple GFP imaging capability after only a brief Nile red staining step in isopropanol. The speed, affordability, and reproducibility of this protocol make it ideally suited for high throughput screens. We also demonstrate a paired method for the biochemical determination of triglycerides and phospholipids using gas chromatography mass-spectrometry. This more rigorous protocol should be used as confirmation of results obtained from the Nile red microscopic lipid determination. We anticipate that these techniques will become new standards in the field of C. elegans metabolic research.

Biochemical and High Throughput Microscopic Assessment of Fat Mass in Caenorhabditis Elegans

We present robust biochemical and microscopic methods for studying Caenorhabditis elegans lipid stores. A rapid, simple, fixing-staining procedure for fluorescent lipid droplet imaging leverages the spectral properties of the lipophilic dye Nile red. We then present biochemical measurement of triglycerides and phospholipids using solid phase extraction and gas chromatography-mass spectrometry.

The nematode C. elegans has emerged as an important  model for the study of conserved genetic pathways regulating fat metabolism as  it relates to human ...

Visualization and Analysis of mRNA Molecules Using Fluorescence In Situ Hybridization in Saccharomyces cerevisiae

The Fluorescence in situ Hybridization (FISH) method allows one to detect nucleic acids in the native cellular environment. Here we provide a protocol for using FISH to quantify the number of mRNAs in single yeast cells. Cells can be grown in any condition of interest and then fixed and made permeable. Subsequently, multiple single-stranded deoxyoligonucleotides conjugated to fluorescent dyes are used to label and visualize mRNAs. Diffraction-limited fluorescence from single mRNA molecules is quantified using a spot-detection algorithm to identify and count the number of mRNAs per cell. While the more standard quantification methods of northern blots, RT-PCR and gene expression microarrays provide information on average mRNAs in the bulk population, FISH facilitates both the counting and localization of these mRNAs in single cells at single-molecule resolution.

Visualization and Analysis of mRNA Molecules Using Fluorescence In Situ Hybridization in Saccharomyces cerevisiae

This protocol describes an experimental procedure for performing Fluorescence in situ Hybridization (FISH) for counting mRNAs in single cells at single-molecule resolution.

The Fluorescence in situ Hybridization (FISH) method allows one to detect nucleic acids in the native cellular environment. Here we provide a protocol for ...

Coupled Assays for Monitoring Protein Refolding in Saccharomyces cerevisiae

Proteostasis, defined as the combined processes of protein folding/biogenesis, refolding/repair, and degradation, is a delicate cellular balance that must be maintained to avoid deleterious consequences 1. External or internal factors that disrupt this balance can lead to protein aggregation, toxicity and cell death. In humans this is a major contributing factor to the symptoms associated with neurodegenerative disorders such as Huntington's, Parkinson's, and Alzheimer's diseases 10. It is therefore essential that the proteins involved in maintenance of proteostasis be identified in order to develop treatments for these debilitating diseases. This article describes techniques for monitoring in vivo protein folding at near-real time resolution using the model protein firefly luciferase fused to green fluorescent protein (FFL-GFP). FFL-GFP is a unique model chimeric protein as the FFL moiety is extremely sensitive to stress-induced misfolding and aggregation, which inactivates the enzyme 12. Luciferase activity is monitored using an enzymatic assay, and the GFP moiety provides a method of visualizing soluble or aggregated FFL using automated microscopy. These coupled methods incorporate two parallel and technically independent approaches to analyze both refolding and functional reactivation of an enzyme after stress. Activity recovery can be directly correlated with kinetics of disaggregation and re-solubilization to better understand how protein quality control factors such as protein chaperones collaborate to perform these functions. In addition, gene deletions or mutations can be used to test contributions of specific proteins or protein subunits to this process. In this article we examine the contributions of the protein disaggregase Hsp104 13, known to partner with the Hsp40/70/nucleotide exchange factor (NEF) refolding system 5, to protein refolding to validate this approach.

Coupled Assays for Monitoring Protein Refolding in Saccharomyces cerevisiae

This article describes the use of a firefly luciferase-GFP fusion protein to investigate in vivo protein folding in Saccharomyces cerevisiae. Using this reagent, refolding of a model heat-denatured protein can be monitored simultaneously by fluorescence microscopy and an enzymatic assay to probe the roles of proteostasis network components in protein quality control.

Proteostasis, defined as the combined processes of protein folding/biogenesis, refolding/repair, and degradation, is a delicate cellular balance that must ...

Purification of the Cystic Fibrosis Transmembrane Conductance Regulator Protein Expressed in Saccharomyces cerevisiae

Defects in the cystic fibrosis transmembrane conductance regulator (CFTR) protein cause cystic fibrosis (CF), an autosomal recessive disease that currently limits the average life expectancy of sufferers to &#60;40 years of age. The development of novel drug molecules to restore the activity of CFTR is an important goal in the treatment CF, and the isolation of functionally active CFTR is a useful step towards achieving this goal.
We describe two methods for the purification of CFTR from a eukaryotic heterologous expression system, S. cerevisiae. Like prokaryotic systems, S. cerevisiae can be rapidly grown in the lab at low cost, but can also traffic and posttranslationally modify large membrane proteins. The selection of detergents for solubilization and purification is a critical step in the purification of any membrane protein. Having screened for the solubility of CFTR in several detergents, we have chosen two contrasting detergents for use in the purification that allow the final CFTR preparation to be tailored to the subsequently planned experiments.
In this method, we provide comparison of the purification of CFTR in dodecyl-&#946;-D-maltoside (DDM) and 1-tetradecanoyl-sn-glycero-3-phospho-(1&#39;-rac-glycerol) (LPG-14). Protein purified in DDM by this method shows ATPase activity in functional assays. Protein purified in LPG-14 shows high purity and yield, can be employed to study post-translational modifications, and can be used for structural methods such as small-angle X-ray scattering and electron microscopy. However it displays significantly lower ATPase activity.

Purification of the Cystic Fibrosis Transmembrane Conductance Regulator Protein Expressed in Saccharomyces cerevisiae

Heterologous expression and purification of the cystic fibrosis transmembrane conductance regulator (CFTR) are significant challenges and limiting factors in the development of drug therapies for cystic fibrosis. This protocol describes two methods for the isolation of milligram quantities of CFTR suitable for functional and structural studies.&#160;

Defects in the cystic fibrosis transmembrane conductance regulator (CFTR) protein cause cystic fibrosis (CF), an autosomal recessive disease that ...

Rapid Identification of Chemical Genetic Interactions in Saccharomyces cerevisiae

Determining the mode of action of bioactive chemicals is of interest to a broad range of academic, pharmaceutical, and industrial scientists. Saccharomyces cerevisiae, or budding yeast, is a model eukaryote for which a complete collection of ~6,000 gene deletion mutants and hypomorphic essential gene mutants are commercially available. These collections of mutants can be used to systematically detect chemical-gene interactions, i.e. genes necessary to tolerate a chemical. This information, in turn, reports on the likely mode of action of the compound. Here we describe a protocol for the rapid identification of chemical-genetic interactions in budding yeast. We demonstrate the method using the chemotherapeutic agent 5-fluorouracil (5-FU), which has a well-defined mechanism of action. Our results show that the nuclear TRAMP RNA exosome and DNA repair enzymes are needed for proliferation in the presence of 5-FU, which is consistent with previous microarray based bar-coding chemical genetic approaches and the knowledge that 5-FU adversely affects both RNA and DNA metabolism. The required validation protocols of these high-throughput screens are also described.

Rapid Identification of Chemical Genetic Interactions in Saccharomyces cerevisiae

Here we present a cost-effective method for defining chemical-genetic interactions in budding yeast. The approach is built on fundamental techniques in yeast molecular biology and is well suited for the mechanistic interrogation of small to medium collections of chemicals and other media environments.