dna-o6-methylguanine : protein-l-cysteine s-methyltransferase , ec 2.1.1.63 ) , a unique dna repair protein present in most organisms , removes the carcinogenic and mutagenic adduct o6-alkylguanine from dna by stoichiometrically accepting the alkyl group on a cysteine residue in a suicide reaction .
C0012854
dna
C0242958
adduct