| Abstrakt: |
The use of transgenic targets for measuring mutant frequencies in mammalian tissue requires an estimate of the mutant frequency that results from recovery of the transgene in bacterial recovery systems. In this study, we have determined the spontaneous mutant frequency, estimated the mutation rate, and ascertained the mutation spectrum for gene Aof ΦX174 grown in E. colistrain CQ2 from 156 small independent cultures. The mutant frequency of 12 of the 156 cultures was 17 ± 1.0 × 10−6and the estimated mutation rate per gene replication was 7.4 ± 2.3 × 10−6. The mutant frequency and spectrum from E. coliwere not significantly different from that of solvent‐treated embryonic mouse cells in culture, 19 ± 0.5 × 10−6(Valentine CR et al. [2002]: Environ Mol Mutagen 39:55–68), indicating that those spontaneous mutants were primarily derived from E. coli. The E. colispectrum was heavily weighted toward two major target sites (hot spots), 4225A→G (56%) and 4218G→A or C (20%). Four new target sites and one new mutational event were recovered by the gene Aforward assay. A mutant spectrum from an expanded phage stock was also determined to assess the effects of propagating the virus. This mutant frequency was higher (6 × 10−4), contained more double mutants (15% compared to 0.6%), and had a significantly different spectrum from the spectrum for independent cultures (fewer A:T→G:C and G:C→C:G changes and more G:C→A:T; P< 0.002). The E. colimutation spectrum will be useful for determining the origin of gene Amutation in tissues of ΦX174 transgenic mice. Environ. Mol. Mutagen. 44:119–127, 2004. Published 2004 Wiley‐Liss, Inc. |
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