Polymerases Leave Fingerprints: Analysis of the Mutational Spectrum in Escherichia coli rpoB To Assess the Role of Polymerase IV in Spontaneous Mutation

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   FIG. 1.

   Distribution of mutations in rpoB that lead to Rif^r in the wild-type strain (CC107) and in a derivative (EW100) carrying dinB-yafNOP on a multicopy plasmid. Similar sample sizes (294 for CC107 and 289 for EW100) were used. Different base substitutions at the same site are indicated by different patterns. The positions of the sites are indicated with numbers above and below (see Table 3) and are not to scale.
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   FIG. 2.

   Distribution of mutations in rpoB that lead to Rif^r in the wild-type strain (CC107) and a derivative (EW101) carrying the dinB gene on a multicopy plasmid. Because different sample sizes are used, the peak heights here represent percentages of the sample size (140 for EW101 and 294 for CC107, with the heights of the EW101 peaks being effectively normalized [by multiplying by 2.1] to fit the CC107 sample size). The vertical axis indicates actual numbers, but the scales of the peak heights differ. This approach allows a visual comparison with Fig. 1. Note that the transversions at site 1576 are prominent in EW101, as they are in EW100 (Fig. 1). In EW101, at site 1576, GC→CG transversions occur in 17 of 140 instances, compared with 5 of 294 instances for CC107, and GC→TA transversions occur in 15 of 140 instances, compared with 4 of 294 instances for CC107.

• American Society for Microbiology