Repair of O6-ethylguanine DNA lesions in isolated cell nuclei. Presence of the activity in the chromatin proteins.
Cell nuclei prepared from rat liver were alkylated in vitro with ethylnitrosourea; the nuclear DNA was found to lose O6-ethylguanine and 7-ethylguanine during a subsequent incubation at 37 degrees C. The rate of O6-ethylguanine loss is comparable to that observed in vivo, indicating that no cytoplasmic component is needed for the repair; no free O6-ethylguanine was found in the incubation medium of the ethylated nuclei. The rate of 7-ethylguanine loss is higher than the spontaneous depurination in vitro and an amount of free 7-ethylguanine equivalent to that lost by the nuclear DNA was found in the incubation medium; these results suggest that this DNA lesion is excised by a DNA glycosylase. The proteins of the chromatin prepared from the isolated nuclei induced the disappearance of O6-ethylguanine from an added ethylated DNA. No free O6-ethylguanine was released indicating that the repair is not catalyzed by a DNA glycosylase; no oligonucleotides enriched in O6-ethylguanine were released either, indicating that the disappearance of O6-ethylguanine from DNA is not the result of the cooperative action of a specific endonuclease and an exonuclease. Activities capable of removing O6-ethylguanine from DNA were found in other cell compartments; most of it, however, is in the nucleus where the main location is chromatin. A pretreatment of the rats with daily low doses of diethylnitrosamine during 3 or 4 weeks increased 2-3-times the repair activity of the chromatin proteins.
D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism*; D055598:Chemical Phenomena; D002621:Chemistry; D002843:Chromatin / Q000378:metabolism*; D002854:Chromatography, Paper; D004260:DNA Repair / Q000187:drug effects; D004052:Diethylnitrosamine / Q000494:pharmacology; D005038:Ethylnitrosourea / Q000494:pharmacology; D006147:Guanine / Q000031:analogs & derivatives* / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains
D002843:Chromatin; D004052:Diethylnitrosamine; C007673:6-ethylguanine; D006147:Guanine; D005038:Ethylnitrosourea