The Cytosine N4-Methyltransferase M.PvuII Also Modifies Adenine Residues

Abstract Methylation of DNA occurs at the C[5] and N[4] positions of cytosine and N[6] of adenine. The chemistry of methylation is similar among methyltransferases specific for cytosineN[4] and adenineN[6]. Moreover these enzymes have similar structures and active sites. Previously it has been demonstrated that the DNA(adenineN[6])methyltransferases M.EcoRV, M.EcoRI, E. coli dam and both domains of M.FokI also modify cytosine residues at the N[4] position [Jeltsch et al., J. Biol. Chem. 274 (1999), 19538 19544]. Here we show that the cytosineN[4] methyltransferase M.PvuII, which modifies the second cytosine in CAGCTG sequences, also methylates adenine residues in CAGATG/ CAGCTG substrates in which the target cytosine is replaced by adenine in one strand of the recognition sequence. Therefore, adenineN[6] and cytosine N[4] methyltransferases have overlapping target base specificities. These results demonstrate that the target base recognition by Nspecific DNA methyltransferases is relaxed in many cases. Furthermore, it shows that the catalytic mechanisms of adenine N[6] and cytosineN[4] methyltransferases are very similar.

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