NEW 5' REGIONS OF THE MURINE AND HUMAN GENES FOR DNA (CYTOSINE-5)-METHYLTRANSFERASE

DNA (cytosine-5)-methyltransferases (EC 2.1.1.37) maintain patterns of methylated cytosine residues in the mammalian genome; faithful mainte nance of methylation patterns is required for normal development of mi ce, and aberrant methylation patterns are associated with certain huma n tumors and developmental abnormalities. The organization of coding s equences at the 5'-end of the murine and human DNA methyltransferase g enes was investigated, and the DNA methyltransferase open reading fram e was found to be longer than previously suspected, Expression of the complete open read ing frame by in vitro transcription-translation and by transfection of expression constructs into COS7 cells resulted in the production of an active DNA methyltransferase of the same apparent mass as the endogenous protein, while translation from the second in- frame ATG codon produced a slightly smaller but fully active protein, Characterization of mRNA 5' sequences and the intron-exon structure of the 5' region of the murine and human genes indicated that a previous ly described promoter element (Rouleau, J., Tanigawa, G., and Szyf, M. (1992) J. Biol, Chen, 267, 7368-7377) actually Lies in an intron that is more than 5 kilobases downstream of the transcription start sites.