title: An unexpected absence of queuosine modification in the tRNAs of an Escherichia coli B strain.
abstract: The post-transcriptional processing of tRNAs decorates them with a number of modified bases important for their biological functions. Queuosine, found in the tRNAs with GUN anticodons (Asp, Asn, His, Tyr), is an extensively modified base whose biosynthetic pathway is still unclear. In this study, it was observed that the tRNA(Tyr) from Escherichia coli B105 (a B strain) migrated faster than that from E. coli CA274 (a K-12 strain) on acid urea gels. The organization of tRNA(Tyr) genes in E. coli B105 was found to be typical of the B strains. Subsequent analysis of tRNA(Tyr) and tRNA(His) from several strains of E. coli on acid urea gels, and modified base analysis of tRNA preparations enriched for tRNA(Tyr), showed that E. coli B105 lacked queuosine in its tRNAs. However, the lack of queuosine in tRNAs was not a common feature of all E. coli B strains. The tgt and queA genes in B105 were shown to be functional by their ability to complement tgt and queA mutant strains. These observations suggested a block at the step of the biosynthesis of preQ(1) (or preQ(0)) in the B105 strain. Interestingly, a multicopy vector harbouring a functional tgt gene was toxic to E. coli B105 but not to CA274. Also, in mixed cultures, E. coli B105 was readily competed out by the CA274 strain. The importance of these observations and this novel strain (E. coli B105) in unravelling the mechanism of preQ(1) or preQ(0) biosynthesis is discussed.
authors.affiliation: Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India1.
authors.forename: T K
authors.initials: TK
authors.lastname: Dineshkumar
authors.affiliation: Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India1.
authors.forename: Swapna
authors.initials: S
authors.lastname: Thanedar
authors.affiliation: Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India1.
authors.forename: C
authors.initials: C
authors.lastname: Subbulakshmi
authors.affiliation: Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India1.
authors.forename: Umesh
authors.initials: U
authors.lastname: Varshney
mesh_terms: D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*; D009704:Nucleoside Q / Q000378:metabolism*; D010430:Pentosyltransferases / Q000378:metabolism; D011744:Pyrimidinones / Q000378:metabolism; D011758:Pyrroles / Q000378:metabolism; D012329:RNA, Bacterial / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012365:RNA, Transfer, Tyr / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014508:Urea
chemical_list: C096876:7-(aminomethyl)-7-deazaguanine; D011744:Pyrimidinones; D011758:Pyrroles; D012329:RNA, Bacterial; D012365:RNA, Transfer, Tyr; D009704:Nucleoside Q; D014508:Urea; D010430:Pentosyltransferases; C020837:queuine tRNA-ribosyltransferase