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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...

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