Isolation and identification by sequence homology of a putative cytosine methyltransferase fromArabidopsis thaliana

A plant cytosine methyltransferase cDNA was isolated using degenerate oligonucleotides, based on homology between prokaryote and mouse methyltransferases, and PCR to amplify a short fragment of a methyltransferase gene. A fragment of the predicted size was amplified from genomlc DNA from Arabidopsis thaliana. Overlapping cDNA clones, some with homology to the PCR amplified fragment, were Identified and sequenced. The assembled nucleic acid sequence Is 4720 bp and encodes a protein of 1534 amlno acids which has significant homology to prokaryote and mammalian cytosine methyltransferases. Like mammalian methylases, this enzyme has a C terminal methyltransferase domain linked to a second larger domain. The Arabidopsis methylase has eight of the ten conserved sequence motifs found in prokaryote cytoslne-5 methyltransferases and shows 50% homology to the murlne enzyme in the methyltransferase domain. The amlno terminal domain is only 24% homologous to the murlne enzyme and lacks the zinc binding region that has been found in methyltransferases from both mouse and man. In contrast to mouse where a single methyltransferase gene has been identified, a small multigene family with homology to the region amplified in PCR has been identified in Arabidopsis thaliana