title: DNA sequence analysis of spontaneous tonB deletion mutations in a polA1 strain of Escherichia coli K12.
abstract: By DNA sequence analysis, we have determined a spectrum of 61 spontaneous mutations occurring in the endogenous tonB gene in the polA1 strain of Escherichia coli. The overall mutation frequency was approximately 2.4-fold higher in the polA1 strain and this was attributable to enhanced rates of deletion and frameshift mutations. Among 39 deletions, a hot spot (17 mutations) was detected: a 13-bp deletion presumably directed by a 3-bp repeated sequence at its end points. The remaining 22 were distributed among 19 different mutations either flanked (16/19) or not flanked (3/19) by repeated sequences. Single-base frameshifts accounted for 8 mutations of either repeated (3/8) or nonrepeated (5/8) bases among which 6 were minus one frameshift. In contrast to previous reports, we did not frequently observe a 5'-GTGG-3' sequence in the vicinity of the deletions and frameshifts. The results presented here indicated an anti-deletion and anti-frameshift role for DNA polymerase I.
authors.affiliation: Graduate School of Science, Tohoku University, Sendai, 980-8578, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Agemizu
authors.forename: N
authors.initials: N
authors.lastname: Uematsu
authors.forename: K
authors.initials: K
authors.lastname: Yamamoto
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D004252:DNA Mutational Analysis; D004256:DNA Polymerase I / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins; D016368:Frameshift Mutation; D017353:Gene Deletion; D008565:Membrane Proteins / Q000235:genetics*; D012091:Repetitive Sequences, Nucleic Acid; D013045:Species Specificity
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; C057616:tonB protein, Bacteria; C489181:tonB protein, E coli; D004256:DNA Polymerase I