Control of vacuole permeability and protein degradation by the cell cycle arrest signal in Saccharomyces cerevisiae

Abstract

S. cerevisiae responds to deprivation of nutrients by arresting cell division at the unbudded G1 stage. Cells situated outside of G1 at the time of deprivation complete the cell cycle before arresting. This prompted an investigation of the source of nutrients used by these cells to complete division and the mechanisms controlling their availability. A close correlation was found between accumulation of unbudded cells and loss of previously formed allophanate hydrolase activity after nutrient starvation. These losses were not specific to the allantoin system, since they were observed for a number of other enzymes and also when cellular protein levels were monitored with [3H]leucine. Loss of hydrolase activity was also observed when protein synthesis was inhibited by addition of inhibitors or loss of the prt1 gene product. Onset of nutrient starvation brought about release of large quantities of arginine and allantoin normally sequestered in the cell vacuole. Treatment of a cells with .alpha.-factor resulted in the release of allantoin and arginine from the cell vacuole and the onset of intracellular protein degradation. These effects were not observed when .alpha. cells or a/.alpha. diploid strains were treated with .alpha.-factor. Release of vacuolar constituents and protein turnover may be regulated by the G1 arrest signal.