Regulation of RNA Synthesis in Yeast: The Stringent Control of Ribosomal RNA Synthesis

Abstract

In procaryotic and yeast cells the restriction of RNA syntheis that occurs on starvation of an auxotrophic strain for required amino acids has been called the stringent control. In response to being deprived of a required amino acid these cells rapidly shut off protein synthesis and synthesis of ribosomal RNA (rRNA) (Shulman et al., 1977). The existence of relaxed mutants relatively unresponsive to amino acid deprivation has led to extensive studies of the molecular mechanism of the stringent control in bacteria. Recently, we isolated and characterized the first relaxed mutant of yeast called Saccharomyces cerevisiae SY15 (Waltschewa et al., 1983). Upon starvation for required tyrosine the SY15 mutant cells synthesize and accumulate rRNA at rates comparable to those in the non-starved controls. In crosses with wild type strains the relaxed phenotype was found to segregate 2:2 demonstrating the existence of one nuclear mutation (designated str) confering the relaxed genotype in the SY15 mutant (Stateva and Venkov, 1984).