Yeast has a true stringent response

Abstract

IN bacteria there is a coordinate regulation of the synthesis of ribosomal RNA and ribosomal protein¹. This is most evident from studies of the rates of synthesis of ribosomal components as a function of the growth rate of the cell^2,3. Another example is the ‘stringent response’, in which cells deprived of an essential amino acid shut down the transcription of ribosomal RNA as well as that of messenger RNA for ribosomal proteins^4,5, but increase the synthesis of mRNA for certain biosynthetic proteins⁶. Although this stringent response is at least partially due to the rc gene product and/or its synthesis of ppGpp, little is known about the detailed mechanisms involved in controlling the two types of transcription. To what degree does the stringent response exist in eukaryotic cells, which use separate polymerases for the transcription of ribosomal RNA and messenger RNA⁶? We⁷ and others⁸ have shown that in Saccharomyces cerevisiae deprived of an amino acid, the transcription of ribosomal RNA is severely inhibited. Ribosomal RNA transcription is also inhibited in cells treated with cycloheximide^7,9, but it continues almost normally in cells in which synthesis of ribosomal proteins has specifically been inhibited through a temperature-sensitive mutation¹⁰. We demonstrate here that in cells deprived of an amino acid there is a specific depletion of messenger RNA coding for ribosomal proteins.