PEPTIDE-MAPPING OF THE MURINE DNA METHYLTRANSFERASE REVEALS A MAJOR PHOSPHORYLATION SITE AND THE START OF TRANSLATION

The murine DNA methyltransferase catalyzes the transfer of methyl grou ps from S-adenosylmethionine to cytosines within d(CpG) dinucleotides. The enzyme is necessary for normal embryonic development and is impli cated in a number of important processes, including the control of gen e expression and cancer, Metabolic labeling and high pressure liquid c hromatography-electrospray ionization-mass spectrometry (HPLC-ESI-MS) were performed on DNA methyltransferase purified from murine erythrole ukemia cells, Serine 514 was identified as a major phosphorylation sit e that lies in a domain required for targeting of the enzyme to the re plication foci, These results present a potential mechanism for the re gulation of DNA methylation. HPLC-ESI-MS peptide mapping data demonstr ated that the purified murine DNA methyltransferase protein contains t he N-terminal regions predicted by the recently revised 5' gene sequen ces (Yoder, J. A., Yen, R.-W. C., Vertino, P. M., Bestor, T. H., and B aylin, S. B. (1996) J. Biol, Chem, 271, 31092-31097), The evidence sug gests a start of translation at the first predicted methionine, with n o alternate translational start sites, Our peptide mapping results pro vide a more detailed structural characterization of the DNA methyltran sferase that will facilitate future structure/function studies.