title: Ribosomes regulate the stability and action of the exoribonuclease RNase R.
abstract: Ribonucleases play an important role in RNA metabolism. Yet, they are also potentially destructive enzymes whose activity must be controlled. Here we describe a novel regulatory mechanism affecting RNase R, a 3' to 5' exoribonuclease able to act on essentially all RNAs including those with extensive secondary structure. Most RNase R is sequestered on ribosomes in growing cells where it is stable and participates in trans-translation. In contrast, the free form of the enzyme, which is deleterious to cells, is extremely unstable, turning over with a half-life of 2 min. RNase R binding to ribosomes is dependent on transfer-messenger RNA (tmRNA)-SmpB, nonstop mRNA, and the modified form of ribosomal protein S12. Degradation of the free form of RNase R also requires tmRNA-SmpB, but this process is independent of ribosomes, indicating two distinct roles for tmRNA-SmpB. Inhibition of RNase R binding to ribosomes leads to slower growth and a massive increase in RNA degradation. These studies indicate a previously unknown role for ribosomes in cellular homeostasis.
authors.affiliation: From the Department of Biochemistry and Molecular Biology, Miller School of Medicine, University of Miami, Miami, Florida 33101.
authors.forename: Wenxing
authors.initials: W
authors.lastname: Liang
authors.forename: Murray P
authors.initials: MP
authors.lastname: Deutscher
mesh_terms: D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D005095:Exoribonucleases / Q000737:chemistry*; D059748:Proteolysis; D012313:RNA / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020871:RNA Stability / Q000235:genetics; D012329:RNA, Bacterial / Q000737:chemistry / Q000235:genetics; D012333:RNA, Messenger / Q000737:chemistry / Q000235:genetics; D016601:RNA-Binding Proteins / Q000378:metabolism; D012269:Ribosomal Proteins / Q000737:chemistry / Q000235:genetics; D012270:Ribosomes / Q000201:enzymology* / Q000235:genetics
chemical_list: D012329:RNA, Bacterial; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D012269:Ribosomal Proteins; C034212:ribosomal protein S12; C430328:small protein B; C096222:tmRNA; D012313:RNA; D005095:Exoribonucleases; C080868:ribonuclease R
keywords: Escherichia coli; Protein Stability; RNA Metabolism; Ribonuclease; Ribosomes