Conserved plant genes with similarity to mammalian de novo DNA methyltransferases

DNA methylation plays a critical role in controlling states of gene activit y in most eukaryotic organisms, and it is essential for proper growth and d evelopment. Patterns of methylation are established by de novo methyltransf erases and maintained by maintenance methyltransferase activities. The Dnmt 3 family of de novo DNA methyltransferases has recently been characterized in animals. Here we describe DNA methyltransferase genes from both Arabidop sis and maize that show a high level of sequence similarity to Dnmt3, sugge sting that they encode plant de novo methyltransferases. Relative to all kn own eukaryotic methyltransferases, these plant proteins contain a novel arr angement of the motifs required for DNA methyltransferase catalytic activit y. The N termini of these methyltransferases contain a series of ubiquitin- associated (UBA) domains. UBA domains are found in several ubiquitin pathwa y proteins and in DNA repair enzymes such as Rad23. and they may be involve d in ubiquitin binding. The presence of UBA domains provides a possible lin k between DNA methylation and ubiquitin/proteasome pathways.