TRANSCRIPTIONAL ACTIVITY OF PANNIER IS REGULATED NEGATIVELY BY HETERODIMERIZATION OF THE GATA DNA-BINDING DOMAIN WITH A COFACTOR ENCODED BYTHE U-SHAPED GENE OF DROSOPHILA

The genes pannier (pnr) and u-shaped (ush) are required for the regula tion of achaete-scute during establishment of the bristle pattern in D rosophila. pnr encodes a protein belonging to the GATA family of trans cription factors, whereas ush encodes a novel zinc finger protein. Gen etic interactions between dominant pnr mutants bearing lesions situate d in the amino-terminal zinc finger of the GATA domain and ush mutants have been described. We show here that both wild-type Pannier and the dominant mutant form activate transcription from the heterologous ru globin promoter when transfected into chicken embryonic fibroblasts. F urthermore, Pnr and Ush are found to heterodimerize through the amino- terminal zinc finger of Pnr and when associated with Ush, the transcri ptional activity of Pnr is lost. In contrast, the mutant pnr protein w ith lesions in this finger associates only poorly with Ush and activat es transcription even when cotransfected with Ush. These interactions have been investigated in vivo by overexpression of the mutant and wil d-type proteins. The results suggest an antagonistic effect of Ush on Pnr function and reveal a new mode of regulation of GATA factors durin g development.