title: 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.
authors.affiliation: Department of Medical Genetics, University of Toronto, Ontario, Canada.
authors.forename: E
authors.initials: E
authors.lastname: Maicas
authors.forename: F G
authors.initials: FG
authors.lastname: Pluthero
authors.forename: J D
authors.initials: JD
authors.lastname: Friesen
mesh_terms: D005786:Gene Expression Regulation; D007700:Kinetics; D008433:Mathematics; D011132:Polyribosomes / Q000378:metabolism; D014176:Protein Biosynthesis; D012331:RNA, Fungal / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D012269:Ribosomal Proteins / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics*
chemical_list: D012331:RNA, Fungal; D012333:RNA, Messenger; D012269:Ribosomal Proteins