Preferential binding of DNA methyltransferase and increased de novo methylation of deoxyinosine containing DNA

Abstract
Mammalian DNA‐cytosine 5‐methyltransferases methylate cytosines in deoxyinosine containing DNA polymers more rapidly than in other synthetic or naturally occurring DNAs. The initial methylation rate of poly(dI‐dC)·poly(dI‐dC) is about 10‐times higher than that of poly‐(dG‐dC)·poly(dG‐dC) or of the native Micrococcus luteus DNA. In competitive binding experiments, DNA methyltransferase has about 10‐fold higher affinity for the dI‐containing alternating DNA polymer than for poly(dG‐dC) · poly(dG‐dC). The observed high methyl accepting capacity of poly(dI‐dC) · poly(dI‐dC) may be a useful methodological advance to determine de novo DNA methyltransferase activity in extracts of mammalian cells.