A system in mouse liver for the repair of O6-methylguanine lesions in methylated DNA.
An activity from mouse liver with catalyzes the disappearance of O6-methylguanine from DNA methylated with methylnitrosourea has been partially purified by ammonium sulfate fractionation and DNA-cellulose chromatography. The activity does not require divalent metal ions and is not affected by EDTA. It is specific for the repair of O6-methylguanine lesions and does not affect the removal of 7-methylguanine, 7-methyladenine or 3-methyladenine. The disappearance of O6-methylguanine is linear with respect to the concentration of protein and is dependent on incubation temperature. The kinetics and substrate dependence experiments suggest that the protein factor is product-inactivated. Amino acid analysis of hydrolysates of protein obtained after incubation of methylated DNA with the protein factor indicates the presence of radiolabeled S-methyl-L-cysteine, suggesting that during the repair of O6-methylguanine from methylated DNA, the methyl group is transferred to a sulfhydryl of a cysteine residue of a protein. This represents the first such demonstration in a mammalian system.
D000596:Amino Acids / Q000032:analysis; D000818:Animals; D004247:DNA / Q000378:metabolism*; D004260:DNA Repair; D006147:Guanine / Q000031:analogs & derivatives* / Q000378:metabolism; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D008297:Male; D008745:Methylation; D008770:Methylnitrosourea / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D011506:Proteins / Q000302:isolation & purification / Q000378:metabolism
D000596:Amino Acids; D011506:Proteins; D006147:Guanine; D008770:Methylnitrosourea; D004247:DNA; C008449:O-(6)-methylguanine