Increased spontaneous reversion of certain frameshift mutations in DNA polymerase I deficient strains of Escherichia...

A tenfold increase in the spontaneous reversion frequency of two of six lacZ frameshift mutations tested was observed in strains containing the following DNA polymerase I mutations--polA1, polA5, polA6, polAex1, res-3 and resA1. Reconstruction experiments indicated that this increase was not the result of a selective effect. Only a fourfold increase in frameshift mutations was found in strains containing a polA107 mutation. Both the polAex1 and polA107 mutations result in defective 5' to 3' exonuclease activity and do not affect polymerizing activity, but have different effects on frameshift mutation. A polA mutation on the chromosome induced frameshift mutations in a gene on an F episome. None of three auxotrophic mutations studied showed high frequency reversion in the presence of the polA1 or polA6 mutations.