ABSTRACT: The nucleotide sequence data reported have been deposited in the DDBJ, EMBL, GenBank(R) and GSDB Nucleotide Sequence Databases under accession numbers AY196089, AY196090, AY376663, AY377920 and AY376664. Recently, a new class of histone methyltransferases that plays an indirect role in chromatin silencing by targeting a conserved lysine residue in the nucleosome core was described, namely the Dot1 (disruptor of telomeric silencing) family [Feng, Wang, Ng, Erdjument-Bromage, Tempst, Struhl and Zhang (2002) Curr. Biol. 12, 1052-1058; van Leeuwen, Gafken and Gottschling (2002) Cell (Cambridge, Mass.) 109, 745-756; Ng, Feng, Wang, Erdjument-Bromage, Tempst, Zhang and Struhl (2002) Genes Dev. 16, 1518-1527]. In the present study, we report the isolation, genomic organization and in vivo express