Methyl methane sulfonate-sensitive mutant of Escherichia coli deficient in an endonuclease specific for apurinic sites in deoxyribonucleic acid

Publisher Website
Google Scholar
Abstract
A methyl methane sulfonate (MMS)-sensitive mutant of E. coli AB 1157 was obtained by N-methyl-N'' -nitro-N-nitrosoguanidine treatment. The mutant strain, AB 3027, is defective both in endonuclease activity for apurinic sites in DNA and in DNA polymerase I, as shown by direct enzyme assays. Derivative strains, which retained the deficiency in endonuclease activity for apurinic sites (approximately 10% of the wild-type enzyme level) but had normal DNA polymerase I activity, were obtained by P1- mediated transduction (strain NH5016) or by selection of revertants to decreased MMS sensitivity. These endonuclease-deficient strains are more MMS-sensitive than wild-type strains. Revertants of these deficient strains to normal MMS resistance were isolated. They had increased levels of the endonuclease activity but did not attain wild-type levels. Endonuclease for apurinic sites, may be active in repair of lesions introduced into DNA as a condequence of MMS treatment. Two different endonucleases that specifically attack DNA containing apurinic sites are present in E. coli K-12. A heat-labile activity, sensitive to inhibition by EDTA, accounts for 90% of the total endonuclease activity for apurinic sites in crude cell extracts. The residual 10% is due to a more heat-resistant activity, refractory to EDTA inhibition. The AB3027 and NH5016 strains have normal amounts of the latter endonuclease but no or very little of the former activity.