title: Endonucleolytic activity directed towards 8-(2-hydroxy-2-propyl) purines in double-stranded DNA.
abstract: Photoalkylation of circular covalently closed DNA from phage PM2 with isopropyl alcohol by using a free radical photoinitiator and UV light of lambda greater than 305 nm led to the specific 8-substitution of purine moieties in the DNA, yielding 8-(2-hydroxy-2-propyl)adenine and 8-(2-hydroxy-2-propyl)guanine as the only detectable damage in the DNA. Using this specifically photoalkylated DNA as a substrate, we discovered in extracts of Micrococcus luteus an endonucleolytic activity that is directed towards 8-(2-hydroxy-2-propyl) purines in DNA. The activity is not a combination of a DNA-glycosylase and an apurinic site endonuclease. It is not inhibited by single-stranded DNA, by UV- or gamma-irradiated single-stranded DNA, or by normal or depurinated double-stranded DNA. however, gamma- or UV-(254 nm) irradiated double-stranded DNAs to inhibit the activity, hinting at the possibility of a common type of lesion in these damaged DNAs. Divalent cations are not required for the incising activity, and it is fully active in 1 mM EDTA, whereas caffeine and ATP cause inhibition. Extracts of mutant M. luteus lacking pyrimidine-dimer-directed endonucleases were found to contain the endonucleolytic activity in levels comparable to those present in the wild type. After the incision, we could demonstrate the specific excision of the 8-alkylated purines from the damaged DNA. The special conformational consequences of the 8-alkylation of purines, at the nucleotide level, namely their nonregular syn conformation, suggest that it is the distortion in the DNA that is recognized by the endonuclease.
mesh_terms: D000478:Alkylation; D004260:DNA Repair; D004270:DNA, Circular / Q000378:metabolism; D003851:Deoxyribonucleases / Q000378:metabolism*; D004720:Endonucleases / Q000378:metabolism*; D008837:Micrococcus / Q000201:enzymology; D011687:Purines; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
chemical_list: D004270:DNA, Circular; D011687:Purines; D003851:Deoxyribonucleases; D004720:Endonucleases