Mutagenesis during transformation of Bacillus subtilis. I. An increase in "selfing' resulting from hybrid donor DNAs.

Reverse mutations increase when competent Bacillus subtilis cells are transformed with high concentrations of homologous "selfer' DNA. A high proportion of the mutants were also transformants of linked genes. A stimulation in the appearance of reversed mutations occurred when homoduplex and heteroduplex "selfer' DNAs were used as donors. Digestions of native and hybrid DNAs with nuclease S1 from Aspergillus oryzae resulted in the preferential decrease of mutations as compared to a much smaller inactivation of single marker transformation. Among various repair-deficient strains of B. subtilis, only poly A mutants showed a preferential effect of either suppressing or stimulating the frequency of reverse mutation induced by "selfer' DNA. The results are consistent with mutagenic errors occurring during gap-filling steps in the process of either mismatch repair or recombinational strand exchanges.