Characterization of human enzymes specific for damaged DNA: resolution of endonuclease for irradiated DNA from an apparent N-glycosidase active on alkylated DNA
Open Access
- 1 January 1977
- journal article
- Published by Oxford University Press (OUP) in Nucleic Acids Research
- Vol. 4 (7) , 2445-2454
- https://doi.org/10.1093/nar/4.7.2445
Abstract
An endonuclease partially purified from human lymphoblasts, and active against ultraviolet-irradiated DNA, was found to act additionally on DNA damaged by either x-radiation or methylmethanesulfonate. To determine if these activities were truly endonucleolytic, the reaction products were analyzed under conditions that prevented conversion of apurinic or apyrimidinic sites to single-strand breaks. With either ultraviolet- or x-irradiated DNA, strand breakage remained maximal, hence confirming the endonucleolytic character of the enzyme. By contrast, with DNA alkylated with methylmethanesulfonate, strand breakage was sharply reduced. Additional experiments indicated that the activity for alkylated DNA induces strand breaks only in concert with a purified endonuclease specific for apurinic sites, suggesting that it is an N-glycosidase that depurinates alkylated bases. This enzyme was separated from the endonuclease specific for irradiated DNA, by chromatography on DNA-agarose.Keywords
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