title: Mutations at three sites in the Escherichia coli 23S ribosomal RNA binding region for protein L11 cause UGA-specific suppression and conditional lethality.
abstract: A single nucleotide change, G to A, at nucleotide position 1093 of E. coli 23S ribosomal RNA was found to cause UGA-specific suppression (D.K. Jemiolo, F.T. Pagel and E.J. Murgola, Proc. Natl. Acad. Sci. USA, in press). To obtain new kinds of UGA-specific suppressors in 23S rRNA, we used segment-directed mutagenic PCR, and targeted first the 1405 nucleotide SnaBI/I-CeuI segment, which includes position 1093, of the rrnB operon cloned into a multicopy plasmid. The mutagenized fragments were subcloned into the plasmid vector and used to transform to ampicillin resistance (Ampr) a recipient strain containing a UGA mutation in trpA. The Ampr transformants were then screened for suppression of UGA. After purification, Trp+ transformants were tested for association of the suppressor phenotype first with the plasmid and then specifically with the SnaBI/I-CeuI fragment. In one screening, four different kinds of mutational change were found, all at three sites within a highly conserved hexanucleotide loop in domain II of 23S rRNA. This region is part of the site for binding of the large subunit protein L11, which has been shown to be involved in peptide chain termination in a specific way. All of the mutants (G1093A, G1093 delta, A1095 delta, and U1097 delta) suppress UGA mutations, but not UAA or UAG mutations, and all four types exhibit high-temperature conditional lethality when highly expressed. Several mechanisms can be suggested for the UGA-specific suppression exhibited by these mutants, including altered interaction with protein L11, Second-site mutations that overcome the conditional lethality of G1093A indicate that intramolecular interactions within 23S rRNA may play a role in peptide chain termination at the UGA stop codon.
authors.affiliation: Department of Molecular Genetics, University of Texas M. D. Anderson Cancer Center, Houston 77030, USA.
authors.forename: E J
authors.initials: EJ
authors.lastname: Murgola
authors.forename: W
authors.initials: W
authors.lastname: Xu
authors.forename: A L
authors.initials: AL
authors.lastname: Arkov
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D018388:Codon, Terminator / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D010443:Peptide Chain Termination, Translational / Q000235:genetics; D010641:Phenotype; D017354:Point Mutation; D012338:RNA, Ribosomal, 23S / Q000235:genetics* / Q000378:metabolism*; D012269:Ribosomal Proteins / Q000378:metabolism*; D013489:Suppression, Genetic; D013696:Temperature
chemical_list: D001426:Bacterial Proteins; D018388:Codon, Terminator; D012338:RNA, Ribosomal, 23S; D012269:Ribosomal Proteins; C027624:ribosomal protein L11