DNA methyltransferase polypeptides in mouse and human cells.

DNA methyltransferase was isolated as a single polypeptide of 190 kDa from mouse P815 mastocytoma cells by immunoaffinity chromatography. This polypeptide seems to be highly susceptible to proteolytic degradation resulting in additional polypeptides in the size range of 150 to 190 kDa. A polypeptide of 190 kDa was immunoprecipitated by monoclonal anti-DNA methyltransferase antibodies from extracts of two different human cell lines, Raji and K562. The 190 kDa polypeptide was synthesized in rapidly proliferating cells and, albeit at a much lower rate, also in cells grown to saturating density. DNA methyltransferase polypeptides smaller than 190 kDa were synthesized neither in log phase nor in stationary phase cells.