Molecular characterization of three rice SET-domain proteins

Methylation of histone H3 at lysine 9 (H3K9) is a critical step for heterochromatin formation, which plays essential roles in genome stability and gene regulation. SU(VAR)3-9 was the first H3K9 methyltransferase identified from mammals. In rice and Arabidopsis, each haploid genome contains 15 genes encoding proteins showing high sequence homology to SU(VAR)3-9, referred here as to SU(VAR)3-9 subfamily genes. Here, we report the characterization of three rice SU(VAR)3-9 subfamily genes, SDG704, SDG706 and SDG714. We show that SDG714 specifically methylates H3K9, whereas SDG704 and SDG706 do not show such activity in our assay conditions. All these three proteins are localized in the nucleus, with SDG704 and SDG714 being stably associated with chromatin during mitosis. Deletion analysis revealed that the C-terminus of SDG714 contains enzyme activity, and that both C- and N-termim of SDG704 and SDG714 are required for chromatin binding. Together, our results uncover a functional diversity for different rice SU(VAR)3-9 subfamily genes. (C) 2007 Elsevier Ireland Ltd. All rights reserved.