THE DROSOPHILA POLYCOMB GROUP GENE PLEIOHOMEOTIC ENCODES A DNA-BINDING PROTEIN WITH HOMOLOGY TO THE TRANSCRIPTION FACTOR YY1

Genes of the Polycomb group (PcG) of Drosophila encode proteins necess ary for the maintenance of transcriptional repression of homeotic gene s. PcG proteins are thought to act by binding as multiprotein complexe s to DNA through Polycomb group response elements (PREs); however, spe cific DNA binding has not been demonstrated for any of the PcG protein s. We have identified a sequence-specific DNA binding protein that int eracts with a PRE from the Drosophila engrailed gene. This protein (PH O) is a homolog of the ubiquitous mammalian transcription factor Yin Y ang-1 and is encoded by pleiohomeotic, a known member of the PcG. We p ropose that PHO acts to anchor PcG protein complexes to DNA.