Abstract
Friend murine erythroleukemia cells were found to contain three distinct species of DNA (cytosine-5-)-methyltransferase (DNA MeTase) whose relative proportions were a characteristic function of the proliferative state of the cells. Rapidly proliferating cells contained a Mr 190,000 species of DNA MeTase (DNA MeTase III), whereas cells in the late logarithmic/early plateau phase of cellular growth contained two species of Mr 150,000 and 175,000 (DNA MeTase I and II); stationary phase cells contained primarily DNA MeTase I. The three species of DNA MeTase displayed structural similarities, as determined by analysis of partial proteolysis products, and have similar de novo sequence specificities in transmethylation reactions involving purified enzyme and prokaryotic DNA. The different relative proportions of the enzymes in cells under different growth conditions suggest that the three species of DNA MeTase fulfill different roles in processes leading to the perpetuation of DNA methylation patterns.