DNA methylation of cytosine nucleotides is an important epigenetic modification 
that occurs in most eukaryotic organisms and is established and maintained by 
various DNA methyltransferases together with their co-factors. There are two 
major categories of DNA methyltransferases: de novo and maintenance. Here, we 
report the isolation and functional characterization of a de novo 
methyltransferase, named OsDRM2, from rice (Oryza sativa L.). The full-length 
coding region of OsDRM2 was cloned and transformed into Escherichia coli and 
Saccharomyces cerevisiae. Both of these organisms expressed the OsDRM2 protein, 
which exhibited stochastic de novo methylation activity in vitro at CG, CHG, and 
CHH di- and tri-nucleotide patterns. Two lines of evidence demonstrated the de 
novo activity of OsDRM2: (1) a 5'-CCGG-3' containing DNA fragment that had been 
pre-treated with OsDRM2 protein expressed in E. coli was protected from 
digestion by the CG-methylation-sensitive isoschizomer HpaII; (2) 
methylation-sensitive amplified polymorphism (MSAP) analysis of S. cerevisiae 
genomic DNA from transformants that had been introduced with OsDRM2 revealed CG 
and CHG methylation levels of 3.92-9.12%, and 2.88-6.93%, respectively, whereas 
the mock control S. cerevisiae DNA did not exhibit cytosine methylation. These 
results were further supported by bisulfite sequencing of the 18S rRNA and EAF5 
genes of the transformed S. cerevisiae, which exhibited different DNA 
methylation patterns, which were observed in the genomic DNA. Our findings 
establish that OsDRM2 is an active de novo DNA methyltransferase gene with 
conserved activity in both prokaryotic and eukaryotic non-host species.