The accumulation of three yeast ribosomal proteins under conditions of excess mRNA is determined primarily by fast protein decay.

Abstract

The suggestion that compensation for overabundant mRNA of the genes for Saccharomyces cerevisiae ribosomal protein (r-protein) L3, L29, or rp59 occurs by translation repression has been reinvestigated. First, analysis of the distribution of these three mRNAs in polysome profiles revealed no differences between normal and mRNA-overproducing strains, indicating that initiation of r-protein translation is not repressed under conditions of mRNA overaccumulation. Second, experiments involving radioactive pulse-labeling of proteins were done by using a modified method of data collection and analysis that allows quantitation and correction for fast decay during the pulse. These measurements revealed that the synthesis rate of the three r-proteins is increased when their mRNA levels are elevated and that their decay rate is also high, with half-lives ranging from a fraction of a minute to more than 10 min. We conclude that accumulation of excess r-protein mRNA has no effect on translation rate; rapid decay of protein during the course of the labeling period can account for the apparent discrepancy between mRNA levels and protein synthesis rates. Yeast r-proteins, when produced in excess, are among the most rapidly degraded proteins so far described.

Complex Regulation of the Yeast Heat Shock Transcription Factor

“…The growth rate dependence of protein synthesis is also reflected in changes in the concentration of rRNA and ribosomal proteins (r-proteins). Because r-proteins are synthesized in excess of what can be assembled into ribosomes (Warner et al, 1985;Maicas et al, 1988), r-proteins represent a major class of short-lived proteins, with half-lives of 1-5 min (Warner, 1989). Therefore, r-proteins represent a second major class of Ssb1/2p substrates.…”

“…In E. coli, some of this regulation is achieved by transcriptional attenuation and translational regulation via binding of ribosomal proteins to the RNAs of target operons (Freedman et al, 1985;Cole and Nomura, 1986). In yeast, regulation is partly transcriptional, via RAP1 and its binding site, the upstream activating sequence (UAS) rpg (Herruer et al, 1987;Moehle and Hinnebusch, 1991;Kraakman et al, 1993), although much of the regulation of ribosomal protein abundance is achieved by a competition between the assembly into ribosomes and the rapid degradation of unassembled ribosomal proteins (Warner et al, 1985;Maicas et al, 1988).Growth rate control clearly modulates the level of the translational machinery, which in turn influences the overall rate of protein synthesis. Changes in the rates of protein synthesis must, in turn, have profound implications for the protein chaperone system.…”

Ribosomal proteins' association with transcription sites peaks at tRNA genes in Schizosaccharomyces pombe

“…Most RPs are very basic (pI > 10), so at high concentrations they might bind nonspecifically to chromatin. Previous studies, however, have indicated that mechanisms that rapidly degrade excess RPs tend to keep the cellular concentrations of free RPs low (Warner 1977(Warner , 1989Maicas et al 1988;Lam et al 2007;Perry 2007).…”

Roles of the negatively charged N-terminal extension of Saccharomyces cerevisiae ribosomal protein S5 revealed by characterization of a yeast strain containing human ribosomal protein S5

“…In eukaryotic cells and particularly in yeast, balanced expression of ribosomal proteins is mainly achieved at the post-transcriptional level and, more specifically, through the regulated turnover of ribosomal proteins (elBaradi et al 1986;Maicas et al 1988;Tsay et al 1988). Thus, individual ribosomal proteins that are present in excess in the cell are rapidly degraded until they reach levels identical to other ribosomal proteins (elBaradi et al 1986;Maicas et al 1988;Tsay et al 1988). The hrpS5 coding sequence was therefore cloned into the high copy number 2m vector to ensure high level hrpS5 expression; the assumption that putative excess hrpS5 would be degraded to maintain hrpS5 at the same level in the mutant strain as yrpS5 in the WT strain was confirmed by Western blotting (see below).…”