In Drosophila, the Polycomb (PcG) gene family encodes chromatin proteins that are required for the repression of homeotic loci in embryonic development. PcG proteins work in conjunction with the trithorax-group (trxG), which activate homeobox gene expression during embryonic development. ENX-1, a mammalian homolog of the Drosophila gene enhancer of zeste, is a PcG protein that is ubiquitously expressed during early embryogenesis and becomes restricted to the central and peripheral nervous systems and sites of fetal hematopoiesis during later development. In the adult, ENX-1 is restricted to specific sites, including spleen, testis and placenta. The gene encoding human ENX-1 transcribes a 746 amino acid polypeptide which contains a trithorax-like domain and a DNA-binding motif. ENX-1 interacts with the proto-oncogene product Vav and is thought to be involved in the proliferation of normal and malignant hematopoietic cells. By altering the regulation of target genes, ENX-1 may also contribute to certain phenotypes of Down syndrome.
