Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
9909137 | Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis | 2005 | 10 Pages |
Abstract
The high fidelity of DNA replication in Escherichia coli is ensured by the α (DnaE) and É (DnaQ) subunits of DNA polymerase providing insertion fidelity, 3â²Â â 5â² exonuclease proofreading activity, and by the dam-directed mismatch repair system. dnaQ49 is a recessive allele that confers a temperature-sensitive proofreading phenotype resulting in a high rate of spontaneous mutations and chronic induction of the SOS response. The aim of this study was to analyse the mutational specificity of dnaQ49 in umuDC and ÎumuDC backgrounds at 28 and 37 °C in a system developed by J.H. Miller. We confirmed that the mutator activity of dnaQ49 was negligible at 28 °C and fully expressed at 37 °C. Of the six possible base pair substitutions, only GC â AT transitions and GC â TA and AT â TA transversions were appreciably increased. However, the most numerous mutations were frameshifts, â1G deletions and +1A insertions. All mutations which increased in response to dnaQ49 damage were to a various extent umuDC-dependent, especially â1G deletions. This type of mutations decreased in CC108dnaQ49ÎumuDC to 10% of the value found in CC108dnaQ49umuDC+ and increased in the presence of plasmids producing UmuDâ²C or UmuDC proteins. In the recovery of dnaQ49 mutator activity the plasmid harbouring umuDâ²C genes was more effective than the one harbouring umuDC. Analysis of mutational specificity of pol III with defective É subunit indicates that continuation of DNA replication is allowed past G:T, C:T, T:T (or C:A, G:A, A:A) mismatches but does not allow for acceptance of T:C, C:C, A:C (or A:G, G:G, T:G) (the underlined base is in the template strand).
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Authors
Anetta Nowosielska, MichaÅ WrzesiÅski, Jadwiga Nieminuszczy, Celina Janion, Elżbieta Grzesiuk,