SUBSTRATE COMPLEXES OF DNA-[N6-ADENINE]-METHYLTRANSFERASES OF T-EVEN PHAGES REGISTERED BY THE GEL RETARDATION METHOD

DNA-[N6-adenine]-methyltransferases of T4 and T2 phages (T4 and T2 MTa ses) recognize in double-stranded DNA palindrome GATC and catalyze the transfer of the methyl group from S-adenosyl-L-methionine (SAM) to po sition N6 of the adenine residue. The gel retardation method was used to study the relative effectiveness of complex formation of T4 and T2 MTases with oligonucleotide substrates of varying length containing GA TC in the middle of the duplex. It is shown that T4 MTase forms stable complexes with 20-mer duplexes bearing a nonmodified or hemimethylate d GATC site. The binding of the duplex to T4 MTase is enhanced in the presence of SAM. Parameters of the interaction of SAM with MTase not b ound and bound with the 20-mer duplex are determined. T2 MTase, which has a higher catalytic activity than the T4 enzyme, forms less stable complexes with oligonucleotides. Thus, there is no direct relation bet ween the stability of the enzyme-substrate complexes and the catalytic activity.