InterPro domain: IPR025778

Members of this family are polycomb group (PcG) proteins from plants. They act as the catalytic subunit of some PcG multiprotein complex, which methylates 'Lys-27' of histone H3, leading to transcriptional repression of the affected target genes. These enzymes are also required to regulate floral development by repressing the AGAMOUS homeotic gene in leaves, inflorescence stems and flowers. They regulate the antero-posterior organisation of the endosperm, as well as the division and elongation rates of leaf cells. PcG proteins act by forming multiprotein complexes, which are required to maintain the transcriptionally repressive state of homeotic genes throughout development. PcG proteins are not required to initiate repression, but to maintain it during later stages of development [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 ].

Methyltransferases (EC [intenz:2.1.1.-]) constitute an important class of enzymes present in every life form. They transfer a methyl group most frequently from S-adenosyl L-methionine (SAM or AdoMet) to a nucleophilic acceptor such as oxygen leading to S-adenosyl-L-homocysteine (AdoHcy) and a methylated molecule [ 10 , 11 , 12 ]. All these enzymes have in common a conserved region of about 130 amino acid residues that allow them to bind SAM [ 13 ]. The substrates that are methylated by these enzymes cover virtually every kind of biomolecules ranging from small molecules, to lipids, proteins and nucleic acids [ 14 , 14 , 14 ]. Methyltransferase are therefore involved in many essential cellular processes including biosynthesis, signal transduction, protein repair, chromatin regulation and gene silencing [ 14 , 14 , 14 ]. More than 230 families of methyltransferases have been described so far, of which more than 220 use SAM as the methyl donor.

1. Maternal control of embryogenesis by MEDEA, a polycomb group gene in Arabidopsis. Science 280, 446-50
2. Control of fertilization-independent endosperm development by the MEDEA polycomb gene in Arabidopsis. Proc. Natl. Acad. Sci. U.S.A. 96, 4186-91
3. Polycomb group genes control pattern formation in plant seed. Curr. Biol. 11, 277-81
4. The Polycomb-group protein MEDEA regulates seed development by controlling expression of the MADS-box gene PHERES1. Genes Dev. 17, 1540-53
5. Identification of new members of Fertilisation Independent Seed Polycomb Group pathway involved in the control of seed development in Arabidopsis thaliana. Development 131, 2971-81
6. The Arabidopsis thaliana MEDEA Polycomb group protein controls expression of PHERES1 by parental imprinting. Nat. Genet. 37, 28-30
7. A Polycomb-group gene regulates homeotic gene expression in Arabidopsis. Nature 386, 44-51
8. The CURLY LEAF gene controls both division and elongation of cells during the expansion of the leaf blade in Arabidopsis thaliana. Planta 206, 175-83
9. Genetic analysis of incurvata mutants reveals three independent genetic operations at work in Arabidopsis leaf morphogenesis. Genetics 156, 1363-77
10. Natural history of S-adenosylmethionine-binding proteins. BMC Struct. Biol. 5, 19
11. Comprehensive structural and substrate specificity classification of the Saccharomyces cerevisiae methyltransferome. PLoS ONE 6, e23168
12. Many paths to methyltransfer: a chronicle of convergence. Trends Biochem. Sci. 28, 329-35
13. Universal catalytic domain structure of AdoMet-dependent methyltransferases. J. Mol. Biol. 247, 16-20