Interactions of the human, rat, Saccharomyces cerevisiae and Escherichia coli 3-methyladenine-DNA glycosylases with DNA containing dIMP residues

In BRA, the deamination of dAMP generates 2'-deoxy-inosine 5'-monophosphate (dIMP), Hypoxanthine (HX) residues are mutagenic since they give rise to A .T-->G.C transition. They are excised, although with different efficiencies , by an activity of the 9-methyl-adenine (3-meAde)-DNA glycosylases from Es cherichia coli (AlkA protein), human cells (ANPG protein), rat cells (APDG protein) and yeast (MAG protein), Comparison of the kinetic constants for t he excision of HX residues by the four enzymes shows that the E.coli and ye ast enzymes are quite inefficient, whereas for the ANPG and the APDG protei ns they repair the HX residues with an efficiency comparable to that of alk ylated bases, which are believed to be the primary substrates of these DNA glycosylases. Since the use of various substrates to monitor the activity o f HX-DNA glycosylases has generated conflicting results, the efficacy of th e four 3-meAde-DNA glycosylases of different origin was compared using thre e different substrates, Moreover, using oligonucleotides containing a singl e dIMP residue, we investigated a putative sequence specificity of the enzy mes involving the bases next to the HX residue, We found up to 2-5-fold dif ference in the rates of HX excision between the various sequences of the ol igo-nucleotides studied, When the dIMP residue was placed opposite to each of the four bases, a preferential recognition of dl:T over dl:dG, dl:dC and dl:dA mismatches was observed for both human (ANPG) and E.coli (AlkA) prot eins, At variance, the yeast MAG protein removed more efficiently HX from a dl:dG over dl:dC, dl:T and dl:dA mismatches.