A Proline-Rich Region in the Zeste Protein Essential for Transvection and white Repression by Zeste¹

Corresponding author: Joseph Jack, Department of Anatomy, MC-3405, University of Connecticut Health Center, 263 Farmington Ave., Farmington, CT 06030, jack{at}panda.uchc.edu (E-mail).

Communicating editor: L. L. SEARLES

The DNA-binding protein encoded by the zeste gene of Drosophila activates transcription and mediates interchromosomal interactions such as transvection. The mutant protein encoded by the zeste¹ (z¹) allele retains the ability to support transvection, but represses white. Similar to transvection, repression requires Zeste-Zeste protein interactions and a second copy of white, either on the homologous chromosome or adjacent on the same chromosome. We characterized two pseudorevertants of z¹ (z^1-35 and z^1-42) and another zeste mutation (z^78c) that represses white. The z¹ lesion alters a lysine residue located between the N-terminal DNA-binding domain and the C-terminal hydrophobic repeats involved in Zeste self-interactions. The z^78c mutation alters a histidine near the site of the z¹ lesion. Both z¹ pseudorevertants retain the z¹ lesion and alter different prolines in a proline-rich region located between the z¹ 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 account 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 z¹, z^78c, and pseudorevertant lesions mediate interactions between Zeste and the maintenance complexes.

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