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キーワード:
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要旨:
Ether-permeabilized (nucleotide-permeable) cells of Escherichia coli show excision repair of their DNA after having been exposed to the carcinogens N-methyl-N-nitrosourea (MeNOUr), N-ethyl-N-nitrosourea (EtNOUr) and methyl methanesulfonate (MeSO2OMe) which are known to bind covalently to DNA. Defect mutations in genes uvrA, uvrB, uvrC, recA, recB, recC and rep did not inhibit this excision repair.
Enzymic activities involved in this repair were identified by measuring size reduction of DNA, DNA degradation to acid-soluble nucleotides and repair polymerization.
1In permeabilized cells methyl and ethyl nitrosourea induced endonucleolytic cleavage of endogenous DNA, as determined by size reduction of denatured DNA in neutral and alkaline sucrose gradients. An enzymic activity from E. coli K-12 cell extracts was purified (greater than 2000-fold) and was found to cleave preferentially methyl-nitrosourea-treated DNA and to convert the methylated supercoiled DNA duplex (RF I) of phage ΦX 174 into the nicked circular form.
2Degradation of alkylated cellular DNA to acid solubility was diminished in a mutant lacking the 5′→3′ exonucleolytic activity of DNA polymerase I but was not affected in a mutant which lacked the DNA polymerizing but retained the 5′→3′ exonucleolytic activity of DNA polymerase I.
3An easily measurable effect is carcinogen-induced repair polymerization, making it suitable for detection of covalent binding of carcinogens and potentially carcinogenic compounds.
