title: RtcB is the RNA ligase component of an Escherichia coli RNA repair operon.
abstract: RNA 2',3'-cyclic phosphate ends play important roles in RNA metabolism as substrates for RNA ligases during tRNA restriction-repair and tRNA splicing. Diverse bacteria from multiple phyla encode a two-component RNA repair cassette, comprising Pnkp (polynucleotide kinase-phosphatase-ligase) and Hen1 (RNA 3'-terminal ribose 2'-O-methyltransferase), that heals and then seals broken tRNAs with 2',3'-cyclic phosphate and 5'-OH ends. The Pnkp-Hen1 repair operon is absent in the majority of bacterial species, thereby raising the prospect that other RNA repair systems might be extant. A candidate component is RNA 3'-phosphate cyclase, a widely distributed enzyme that transforms RNA 3'-monophosphate termini into 2',3'-cyclic phosphates but cannot seal the ends it produces. Escherichia coli RNA cyclase (RtcA) is encoded in a σ(54)-regulated operon with RtcB, a protein of unknown function. Taking a cue from Pnkp-Hen1, we purified E. coli RtcB and tested it for RNA ligase activity. We report that RtcB per se seals broken tRNA-like stem-loop structures with 2',3'-cyclic phosphate and 5'-OH ends to form a splice junction with a 2'-OH, 3',5'-phosphodiester. We speculate that: (i) RtcB might afford bacteria a means to recover from stress-induced RNA damage; and (ii) RtcB homologs might catalyze tRNA repair or splicing reactions in archaea and eukarya.
authors.affiliation: From the Molecular Biology Program, Sloan-Kettering Institute, New York, New York 10065.
authors.forename: Naoko
authors.initials: N
authors.lastname: Tanaka
authors.affiliation: From the Molecular Biology Program, Sloan-Kettering Institute, New York, New York 10065. Electronic address: s-shuman@ski.mskcc.org.
authors.forename: Stewart
authors.initials: S
authors.lastname: Shuman
mesh_terms: D002384:Catalysis; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D009876:Operon / Q000502:physiology*; D026721:RNA 3' End Processing / Q000502:physiology*; D011130:RNA Ligase (ATP) / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D012329:RNA, Bacterial / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D012343:RNA, Transfer / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D029968:Escherichia coli Proteins; D012329:RNA, Bacterial; D012343:RNA, Transfer; D011130:RNA Ligase (ATP)