Abstract
In plant DNA, cytosines in asymmetric CpNpN are frequently methylated, and genetic analysis suggested that the responsible enzyme is domains rearranged methyltransferase (DRM). We have obtained a tobacco cDNA, which encoded a novel protein consisting of 608 amino acids. Homology search indicated it to resemble DRMs found in maize and Arabidopsis, and designated as NtDRM1. The protein was localized exclusively in the nucleus. Upon expression in Sf9 cells, NtDRM1 exhibited de novo methylation activity towards synthetic as well as native DNA samples, yielding solely 5-methylcytosine. Further analysis for sequence specificity revealed NtDRM1 to preferentially methylate cytosines in CpNpN. Since methylation of CpNpN is proposed to function in epigenetic gene silencing, the present results suggest that NtDRM1, a plant-specific CpNpN-methylase, may play a critical role in regulation of gene expression in response to environmental cues.
