The entire DNA sequence of chromosome III of the yeast Saccharomyces cerevisiae has been determined. This is the first complete sequence analysis of an entire chromosome from any organism. The 315-kilobase sequence reveals 182 open reading frames for proteins longer than 100 amino acids, of which 37 correspond to known genes and 29 more show some similarity to sequences in databases. Of 55 new open reading frames analysed by gene disruption, three are essential genes; of 42 non-essential genes that were tested, 14 show some discernible effect on phenotype and the remaining 28 have no overt function.

Mutations in genes necessary for survival in stationary phase were isolated to understand the ability of wild-type Saccharomyces cerevisiae to remain viable during prolonged periods of nutritional deprivation. Here we report results concerning one of these mutants, rvsl67, which shows reduced viability and abnormal cell morphology upon carbon and nitrogen starvation. The mutant exhibits the same response when cells are grown in high salt concentrations and other unfavorable growth conditions. The RVS167 gene product displays significant homology with the Rvs161 protein and contains a SH3 domain at the C-terminal end. Abnormal actin distribution is associated with the mutant phenotype. In addition, while the budding pattern of haploid strains remains axial in standard growth conditions, the budding pattern of diploid mutant strains is random. The gene RVS167 therefore could be implicated in cytoskeletal reorganization in response to environmental stresses and could act in the budding site selection mechanism.In Saccharomyces cerevisiae, nutrient availability coordinates cell growth and proliferation. In medium containing all essential growth elements, yeast cells proliferate and cell growth and division are held in balance by the necessity of a minimum cell size before beginning a new division cycle (36). If one of the essential elements, for example, carbon or nitrogen, becomes exhausted, yeast cells stop division in the nonbudding G1 phase of the cell cycle (81). The culture then is in stationary phase, and cells can remain in the living state for prolonged periods under conditions which are not propitious for growth. Indeed, in their natural environment, yeast cells spend only a small fraction of their existence in exponential growth, because of the limited availability of nutriments.The transition from exponentially growing cells to arrested stationary-phase cells following nutrient starvation is accompanied by a number of molecular and physiological changes. At the molecular level, accumulation of glycogen and trehalose (48) is observed. The global analysis of proteins synthesized under starvation conditions reveals a subset of proteins whose synthesis increases in nutritional deprivation (9, 32). In addition, synthesis of most of the proteins expressed during exponential phase ceases (9). Physiological changes concern a higher resistance to heat shock (60), to lytic enzymes (20), and to a large number of other environmental stresses.There are mainly two questions related to stationaryphase entry. The first question concerns the mechanisms implied in cell proliferation control in response to the nutrient starvation. Some of the molecular regulatory elements of cell proliferation control are now relatively well-known in S. cerevisiae. Thus a multitude of observations has been taken as evidence that the cyclic AMP (cAMP) pathway could be a signal-transmitting pathway for growth arrest following nutrient exhaustion (35,50,77 sponding to the nutritional environment. Genetic evidence for the existence of at least...

The actin cytoskeleton cells is altered in rvs161 mutant yeast, with the defect becoming more pronounced under unfavorable growth conditions, as described for the rvs167 mutant. The cytoskeletal alteration has no apparent effect on invertase secretion and polarized growth. Mutations in RVS161, just as in RVS167, lead to a random budding pattern in a/alpha diploid cells. This behavior is not observed in a/a diploid cells homozygous for the rvs161-1 or rvs167-1 mutations. In addition, sequence comparisons revealed that amphiphysin, a protein first found in synaptic vesicles of chicken and shown to be the autoantigen of Stiff Man syndrome, presents similarity with both Rvs proteins. Furthermore, limited similarities with myosin heavy chain and tropomyosin alpha chain from higher eukaryotic cells allow for the definition of a possible consensus sequence. The finding of related sequences suggests the existence of a function for these proteins that is conserved among eukaryotic organisms.

In yeast, nutrient starvation leads to entry into stationary phase. Mutants that do not respond properly to starvation conditions have been isolated in Saccharomyces cerevisiae. Among them the rvs161 mutant (RVS for Reduced Viability upon Starvation) is sensitive to carbon, nitrogen and sulphur starvation. When these nutrients are depleted in the medium, mutant cells show cellular viability loss with morphological changes. The mutation rvs161-1 is very pleiotropic, and besides the defects in stationary phase entry, the mutant strain presents other alterations: sensitivity to high salt concentrations, hypersensitivity to amino acid analogs, no growth on lactate or acetate medium. The addition of salts or amino acid analogs leads to the same morphological defects observed in starved cells, suggesting that the gene could be implicated mainly in the control of cellular viability. The gene RVS161 was cloned; it codes for a 30,252 daltons protein. No homology was detected with the proteins contained in the databases. Moreover, Southern analysis revealed the presence of other sequences homologous to the RVS161 gene in the yeast genome.