Yoder J A, Yen R W, Vertino P M, Bestor T H, Baylin S B
Department of Genetics and Development, College of Physicians and Surgeons of Columbia University, New York, New York 10032, USA.
J Biol Chem. 1996 Dec 6;271(49):31092-7. doi: 10.1074/jbc.271.49.31092.
DNA (cytosine-5)-methyltransferases (EC 2.1.1.37) maintain patterns of methylated cytosine residues in the mammalian genome; faithful maintenance of methylation patterns is required for normal development of mice, and aberrant methylation patterns are associated with certain human tumors and developmental abnormalities. The organization of coding sequences at the 5'-end of the murine and human DNA methyltransferase genes was investigated, and the DNA methyltransferase open reading frame was found to be longer than previously suspected. Expression of the complete open reading 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 previously described promoter element (Rouleau, J., Tanigawa, G., and Szyf, M. (1992) J. Biol. Chem. 267, 7368-7377) actually lies in an intron that is more than 5 kilobases downstream of the transcription start sites.
DNA（胞嘧啶-5）-甲基转移酶（EC 2.1.1.37）维持哺乳动物基因组中甲基化胞嘧啶残基的模式；小鼠的正常发育需要甲基化模式的忠实维持，而异常的甲基化模式与某些人类肿瘤和发育异常有关。对小鼠和人类DNA甲基转移酶基因5'端编码序列的组织进行了研究，发现DNA甲基转移酶开放阅读框比以前怀疑的要长。通过体外转录-翻译以及将表达构建体转染到COS7细胞中来表达完整的开放阅读框，产生了一种与内源性蛋白质表观质量相同的活性DNA甲基转移酶，而从第二个符合读码框的ATG密码子进行翻译则产生了一种稍小但完全有活性的蛋白质。对小鼠和人类基因mRNA 5'序列以及5'区域内含子-外显子结构的表征表明，先前描述的启动子元件（Rouleau, J., Tanigawa, G., and Szyf, M. (1992) J. Biol. Chem. 267, 7368-7377）实际上位于转录起始位点下游超过5千碱基的一个内含子中。
