EZH1 is a human homolog of the Drosophila gene Enhancer of zeste E(z), a member of the polycomb group of transcriptional repressors. In mice, EZH1 is a regulator of homeotic gene expression implicated in the assembly of repressive protein complexes in chromatin. The strong sequence conservation between species sμggests potential role for EZH1 in human development as a transcriptional regulator and as a component of protein complexes that stably maintain heterochromatin.