Frame-shift mutants induced by quinacrine are recognized by the mismatch repair system in Streptococcus pneumoniae.

We describe the isolation of amethopterin-resistant mutants induced by quinacrine treatment of exponentially growing cultures of Streptococcus pneumoniae. Only mutants located by recombination analysis in a few hundred base pairs were further studied. They were cloned and their DNA sequences show that most of them are +/-1-base frame-shift mutants. They are excised and repaired to a degree similar to transition mutants (low efficiency class), suggesting that the mismatches resulting from a transition or a +/-1-base mutation are similar substrates for the Hex mismatch repair system.