RNA recognition motif in the Set1-like family of histone-lysine N-methyltransferases
This subfamily corresponds to the RRM of the Set1-like family of histone-lysine N-methyltransferases which includes Set1A and Set1B that are ubiquitously expressed vertebrates histone methyltransferases exhibiting high homology to yeast Set1. Set1A and Set1B proteins exhibit a largely non-overlapping subnuclear distribution in euchromatic nuclear speckles, strongly suggesting that they bind to a unique set of target genes and thus make non-redundant contributions to the epigenetic control of chromatin structure and gene expression. With the exception of the catalytic component, the subunit composition of the Set1A and Set1B histone methyltransferase complexes are identical. Each complex contains six human homologs of the yeast Set1/COMPASS complex, including Set1A or Set1B, Ash2 (homologous to yeast Bre2), CXXC finger protein 1 (CFP1; homologous to yeast Spp1), Rbbp5 (homologous to yeast Swd1), Wdr5 (homologous to yeast Swd3), and Wdr82 (homologous to yeast Swd2). The genomic targeting of these complexes is determined by the identity of the catalytic subunit present in each histone methyltransferase complex. Thus, the Set1A and Set1B complexes may exhibit both overlapping and non-redundant properties. Both Set1A and Set1B contain an N-terminal RNA recognition motif (RRM), also termed RBD (RNA binding domain) or RNP (ribonucleoprotein domain), an N- SET domain, and a C-terminal catalytic SET domain followed by a post-SET domain. In contrast to Set1B, Set1A additionally contains an HCF-1 binding motif that interacts with HCF-1 in vivo.