Pipsqueak and GAGA factor act in concert as partners at homeotic and many other loci.

The Drosophila GAGA factor (GAF) controls transcription and other chromosome functions by altering chromatin structure. We found that a second GAGA-binding protein of Drosophila, Pipsqueak (Psq), can directly bind to GAF and is associated with GAF in vivo. Genetic interaction studies provide evidence that Psq and GAF act together in the transcriptional activation and silencing of homeotic genes. A complete colocalization of Psq and GAF on polytene interphase chromosomes and mitotic chromosomes suggests that the two proteins cooperate as general partners not only at homeotic loci, but also at hundreds of other chromosomal sites.