Mutations in Escherichia coli altering an apurinic endonuclease, endonuclease II, and exonuclease III and their effect on in vivo sensitivity to methylmethanesulfonate.

The levels of endonuclease II, an apurinic endonuclease, and exonuclease III in the parent strains (AB 1157) of Escherichia coli and in various mutants were determined by chromatography on DEAE-cellulose. AB 3027 and NH 5016 lacked endonuclease II and exonuclease III. BW 2001 lacked the apurinic endonuclease and exonuclease III while BW 2007, BW 9093, and BW 9059 lacked only exonuclease III. Deletion mutants BW 9101 and BW 9109 lacked all three enzymes. The latter mutants locate the genes for the two endonucleases in the region of exonuclease III (chith) of 38.2 min (White et al., 1976). All of the mutants which were sensitive to methylmethanesulfonate in vivo lacked exonuclease III, but not all mutants lacking exonuclease III were MMS sensitive. The deletion mutants and NH 5016 were the exceptions.