Proteome studies of Saccharomyces cerevisiae: identification and characterization of abundant proteins.

Two-dimensional (2-D) gel electrophoresis can now be coupled with protein identification techniques and genome sequence information for direct detection, identification, and characterization of large numbers of proteins from microbial organisms. 2-D electrophoresis, and new protein identification techniques such as amino acid composition, are proteome research techniques in that they allow direct characterization of many proteins at the same time. Another new tool important for yeast proteome research is the Yeast Protein Database (YPD), which provides the sequence-derived protein properties needed for spot identification and tabulations of the currently known properties of the yeast proteins. Studies presented here extend the yeast 2-D protein map to 169 identified spots based upon the recent completion of the yeast genome sequence, and they show that methods of spot identification based on predicted isoelectric point, predicted molecular mass, and determination of partial amino acid composition from radiolabeled gels are powerful enough for the identification of at least 80% of the spots representing abundant proteins. Comparison of proteins predicted by YPD to be detectable on 2-D gels based on calculated molecular mass, isoelectric point and codon bias (a predictor of abundance) with proteins identified in this study suggests that many glycoproteins and integral membrane proteins are missing from the 2-D gel patterns. Using the 2-D gel map and the information available in YDP, 2-D gel experiments were analyzed to characterize the yeast proteins associated with: (i) an environmental change (heat shock), (ii) a temperature-sensitive mutation (the prp2 mRNA splicing mutant), (iii) a mutation affecting post-translational modification (N-terminal acetylation), and (iv) a purified subcellular fraction (the ribosomal proteins). The methods used here should allow future extension of these studies to many more proteins of the yeast proteome.