Repair of O6-methylguanine and O4-methylthymine by the human and rat O6-methylguanine-DNA methyltransferases.
In order to compare the ability of the human and rat O6-methylguanine-DNA methyltransferases (transferases) to repair in vitro O6-methylguanine (O6-MeGua) and O4-methylthymine (O4-MeThy) residues, which are two mutagenic DNA adducts formed by alkylating agents, we have purified both proteins to homogeneity. Gel electrophoresis of the proteins shows that the O4-MeThy repair is due to the transfer of the methyl group from the alkylated base to the transferase molecules. However, both proteins repair with different efficiencies the O6-MeGua and O4-MeThy residues present in alkylated DNA, poly[d(G.C)], poly(dG.dC), or in alkylated poly[d(A.T)] and poly(dA.dT), respectively. Reaction of both proteins with either methylated residues follows a second-order kinetics. The rate constants are 1 x 10(9) M-1 min-1 for both proteins acting on O6-MeGua and 4.8 x 10(6) or 1.8 x 10(5) M-1 min-1 for the rat or human protein acting on O4-MeThy, respectively. The activity of the mammalian transferases on O4-MeThy present in a poly(dA.dT) substrate is inhibited by double-stranded DNA.
Zak
P
P
Groupe Radiochimie de l'ADN, Unité 247, Institut Gustave Roussy, Villejuif, France.
Kleibl
K
K
Laval
F
F
D000818:Animals; D004247:DNA / Q000494:pharmacology; D004260:DNA Repair; D004591:Electrophoresis, Polyacrylamide Gel; D006147:Guanine / Q000031:analogs & derivatives* / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008780:Methyltransferases / Q000302:isolation & purification / Q000378:metabolism*; D019853:O(6)-Methylguanine-DNA Methyltransferase; D051381:Rats; D013941:Thymine / Q000031:analogs & derivatives* / Q000378:metabolism
C021223:O-4-methylthymine; D006147:Guanine; D004247:DNA; C008449:O-(6)-methylguanine; D008780:Methyltransferases; D019853:O(6)-Methylguanine-DNA Methyltransferase; D013941:Thymine