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Directionality of DNA replication fork movement strongly affects the generation of spontaneous mutations in Escherichia coli

2001; Elsevier BV; Volume: 307; Issue: 5 Linguagem: Inglês

10.1006/jmbi.2001.4557

1089-8638

Kaoru Yoshiyama, Kumiko Higuchi, Hironobu Matsumura, Hisaji Maki,

Genetic factors in colorectal cancer

Using a pair of plasmids carrying the rpsL target sequence in different orientations to the replication origin, we analyzed a large number of forward mutations generated in wild-type and mismatch-repair deficient (MMR−) Escherichia coli cells to assess the effects of directionality of replication-fork movement on spontaneous mutagenesis and the generation of replication error. All classes of the mutations found in wild-type cells but not MMR− cells were strongly affected by the directionality of replication fork movement. It also appeared that the directionality of replication-fork movement governs the directionality of sequence substitution mutagenesis, which occurred in wild-type cells at a frequency comparable to base substitutions and single-base frameshift mutations. A very strong orientation-dependent hot-spot site for single-base frameshift mutations was discovered and demonstrated to be caused by the same process involved in sequence substitution mutagenesis. It is surprising that dnaE173, a potent mutator mutation specific for sequence substitution as well as single-base frameshift, did not enhance the frequency of the hot-spot frameshift mutation. Furthermore, the frequency of the hot-spot frameshift mutation was unchanged in the MMR− strain, whereas the mutHLS-dependent mismatch repair system efficiently suppressed the generation of single-base frameshift mutations. These results suggested that the hot-spot frameshift mutagenesis might be initiated at a particular location containing a DNA lesion, and thereby produce a premutagenic replication intermediate resistant to MMR. Significant numbers of spontaneous single-base frameshift mutations are probably caused by similar mechanisms.