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  • Title: The cytosine N4-methyltransferase M.PvuII also modifies adenine residues.
    Author: Jeltsch A.
    Journal: Biol Chem; 2001 Apr; 382(4):707-10. PubMed ID: 11405235.
    Abstract:
    Methylation of DNA occurs at the C5 and N4 positions of cytosine and N6 of adenine. The chemistry of methylation is similar among methyltransferases specific for cytosine-N4 and adenine-N6. Moreover these enzymes have similar structures and active sites. Previously it has been demonstrated that the DNA-(adenine-N6)-methyltransferases M.EcoRV, M.EcoRI, E. coli dam and both domains of M.FokI also modify cytosine residues at the N4 position [Jeltsch et al., J. Biol. Chem. 274 (1999), 19538-19544]. Here we show that the cytosine-N4 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, adenine-N6 and cytosine-N4 methyltransferases have overlapping target base specificities. These results demonstrate that the target base recognition by N-specific DNA methyltransferases is relaxed in many cases. Furthermore, it shows that the catalytic mechanisms of adenine-N6 and cytosine-N4 methyltransferases are very similar.
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