THE GAGA FACTOR IS REQUIRED IN THE EARLY DROSOPHILA EMBRYO NOT ONLY FOR TRANSCRIPTIONAL REGULATION BUT ALSO FOR NUCLEAR DIVISION

The GAGA protein of Drosophila was first identified as a stimulatory f actor in in vitro transcription assays using the engrailed and Ultrabi thorax promoters, Subsequent studies have suggested that the GAGA fact or promotes transcription by blocking the repressive effects of histon es; moreover, it has been shown to function in chromatin remodeling, a cting together with other factors in the formation of nuclease hyperse nsitive sites in vitro. The GAGA factor is encoded by the Trithorax-li ke locus and in the studies reported here we have used the maternal ef fect allele Trl(13C) to examine the functions of the protein during em bryogenesis. We find that GAGA is required for the proper expression o f a variety of developmental loci that contain GAGA binding sites in t heir upstream regulatory regions, The observed disruptions in gene exp ression are consistent with those expected for a factor involved in ch romatin remodeling, In addition to facilitating gene expression, the G AGA factor appears to have a more global role in chromosome structure and function. This is suggested by the spectrum of nuclear cleavage cy cle defects observed in Trl(13C) embryos, These defects include asynch rony in the cleavage cycles, failure in chromosome condensation, abnor mal chromosome segregation and chromosome fragmentation, These defects are likely to be related to the association of the GAGA protein with heterochromatic satellite sequences which is observed throughout the c ell cycle.