Studies have been carried out on the effects of mutations in nine distinct genes which regulate ribosome biosynthesis in yeast. Although some mutants have more extensive effects than others, in each case there is an inhibition by 50 to 80% of the synthesis of ribosomal precursor RNA. In each case there is an inhibition of the processing of that RNA which is made, ranging from 80 to 95%. In each case there is degradation of 50 to 70% of that RNA which is processed. Much of the RNA which survives to become the mature 25 s and 18 s species is found in functioning polyribosomes. In three of the mutants, ribosomal protein synthesis has been examined. At the restrictive temperature there is a rapid decline in the synthesis of ribosomal proteins to about 25% of normal. The rate of decline is several-fold faster than the average rate of messenger RNA degradation, leading to the possibility that there is some translational control of this synthesis. The inhibition of ribosome synthesis has enabled us to demonstrate that three proteins become associated with the 60 s subunit only after it reaches the cytoplasm. In none of the mutants is there any accumulation of precursor RNA, of defective precursor particles, or of one of the mature ribosomal subunits. We conclude that there is a stringent regulation of all facets of ribosome biosynthesis in yeast. An interruption at any step rapidly causes a feedback inhibition of all other steps.

• PMID: 4557193
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Journal Article

Authors

Warner JR, Udem SA

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