A PROLINE-RICH REGION IN THE ZESTE PROTEIN ESSENTIAL FOR TRANSVECTIONAND WHITE REPRESSION BY ZESTE

The DNA-binding protein encoded by the zeste gene of Drosophila activa tes transcription and mediates interchromosomal interactions such as t ransvection. The mutant protein encoded by the zeste(1) (z(1)) allele retains the ability to support transvection, but represses white. Simi lar to transvection, repression requires Zeste-Zeste protein interacti ons and a second copy of white, either on the homologous chromosome or adjacent on the same chromosome. We characterized two pseudorevertant s of z(1) (z(1-35) and z(1-42)) and another zeste mutation (z(78c)) th at represses white. The z(1) lesion alters a lysine residue located be tween the N-terminal DNA-binding domain and the C-terminal hydrophobic repeats involved in Zeste self-interactions. The z(78c) mutation alte rs a histidine near the site of the z(1) lesion. Both z(1) pseudorever tants retain the z(1) lesion and alter different prolines in a proline -rich region located between the z(1) lesion and the self-interaction domain. The pseudorevertants retain the ability to self-interact, but fail to repress white or support transvection at Ultrabithorax. To acc ount for these observations and evidence indicating that Zeste affects gene expression through Polycomb group (Pc-G) protein complexes that epigenetically maintain chromatin states, we suggest that the regions affected by the z(1), z(78c), and pseudorevertant lesions mediate inte ractions between Zeste and the maintenance complexes.