Increased rate of base substitution in a hamster mutator strain obtained during serial selection for gene amplification.

The pattern of mutations produced by a mutator gene (obtained during serial selection for amplification of the dihydrofolate reductase [dhfr] locus) shows a pronounced shift from that found in wild-type cells. The rate of certain types of base substitutions (particularly transitions) is dramatically increased, while gene rearrangements constitute a lower proportion of mutations. These data suggest a lower fidelity of the replication process in the mutator strain.