INFLUENCE OF DNA-REPAIR BY ADA AND OGT ALKYLTRANSFERASES ON THE MUTATIONAL SPECIFICITY OF ALKYLATING-AGENTS

作者：ROLDANARJONA T; LUQUEROMERO FL; ARIZA RR; JURADO J; PUEYO C

来源：Molecular Carcinogenesis, 1994, 9(4): 200-209.

DOI：10.1002/mc.2940090404

• SUPF
• IN VIVO MUTAGENESIS
• IN VITRO MUTAGENESIS
• SHUTTLE VECTOR
• MUTATIONAL SPECTRA

We investigated the influence of the alkyltransferases (ATases) encoded by the ada and ogt genes of Escherichia coli on the mutational specificity of alkylating agents. A new mutational assay for selection of supF(-) mutations in shuttle-vector plasmids was used. Treating plasmid-bearing bacteria with N-methyl-N-nitrosourea (MNU), N-ethyl-N-nitrosourea (ENU), and ethyl methanesulfonate (EMS) dramatically increased the mutation frequency (from 33-fold to 789-fold). The vast majority of mutations (89-100%) were G:C-->A:T transitions. This type of mutation increased in ada(-) (MNU) or ogt(-) (ENU) bacteria, suggesting that repair of O-6-methylguanine by ada ATase and repair of O-6-ethylguanine by ogt ATase contribute mainly to the decrease in G:C-->A:T transitions. The analysis of neighboring base sequences revealed an overabundance of G:C-->A:T transitions at 5'-GG sequences. The 5'-PuG bias increased in ATase-defective cells, suggesting that these sequences were not refractory to repair. G:C-->A:T transitions occurred preferentially in the untranscribed strand after in vivo exposure. That this strand specificity was detected even in bacteria devoid of ATase activity (ada(-) ogt(-)) and not after in vitro mutagenesis suggests a bias for damage induction rather than for DNA repair. Highly significant differences were found between the in vivo and in vitro incidences of G:C-->A:T substitutions at the two major hotspots, positions 123 (5'-GGG-3'; antisense strand) and 168 (5'-GGA-3'; sense strand). These results are explained by differences in the probability of formation of stem-loop structures in vivo and in vitro.

• 出版日期1994-4