Direct interaction of the Polycomb protein with Antennapedia regulatory sequences in polytene chromosomes of Drosophila melanogaster.

The Polycomb (Pc) gene is responsible for the elaboration and maintenance of the expression pattern of the homeotic genes during development of Drosophila. In mutant Pc- embryos, homeotic transcripts are ectopically expressed, leading to abdominal transformations in all segments. From this it was suggested that PC+ acts as a repressor of homeotic gene transcription. We have mapped the cis-acting control sequences of the homeotic Antennapedia (Antp) gene regulated by Pc. Using Antp P1 and P2 promoter fragments linked to the E. coli lacZ reporter gene we show different expression patterns of beta-galactosidase (beta-gal) in transformed Pc+ and Pc- embryos. In addition we are able to visualize by immunocytochemical techniques on polytene chromosomes the direct binding of the Pc protein to the transposed cis-regulatory promoter fragments. However, short Antp P1 promoter constructs which are--due to position effects--ectopically activated in salivary glands, do not reveal a Pc binding signal.