Yeasts are free-living, unicellular eukaryotes--fungi. Yet despite their simplicity, yeast cells are similar to higher eukaryotes in several important ways.1 For example, they contain membrane-bound subcellular organelles and possess a similar cytoskeletal organization. In addition, the chromosomal structure of yeast DNA is comparable to that found in higher eukaryotes, with similar mechanics, except that no histone H1 is present.
It is believed that the mechanisms of transcriptional activation and repression are also conserved in yeast and higher eukaryotes, and, like those of other eukaryotes, yeast mRNA transcripts are capped and polyadenylated. Similarly, the proteolytic cleavage of precursor proteins and the secretion of these proteins in yeast show many similarities to those of higher eukaryotes. Finally, a large number of homologous proteins in yeasts and mammals share high DNA sequence and functional identity. The mammalian small G-protein Ras, for example, can complement yeast RAS in a RAS-deficient yeast strain.1 In fact, ...
