CHANGES IN CHROMOSOMAL LOCALIZATION OF HETEROCHROMATIN-BINDING PROTEINS DURING THE CELL-CYCLE IN DROSOPHILA

We examined the heterochromatic binding of GAGA factor and proliferati on disrupter (Prod) proteins during the cell cycle in Drosophila melan ogaster and sibling species. GAGA factor binding to the brown(Dominant ) AG-rich satellite sequence insertion was seen at metaphase, however, no binding of GAGA factor to AG-rich sequences was observed at interp hase in polytene or diploid nuclei. Comparable mitosis-specific bindin g was found for Prod protein to its target satellite in pericentric he terochromatin. At interphase, these proteins bind numerous dispersed s ites in euchromatin, indicating that they move from euchromatin to het erochromatin and back every cell cycle. The presence of Prod in hetero chromatin for a longer portion of the cell cycle than GAGA factor sugg ests that they cycle between euchromatin and heterochromatin independe ntly. We propose that movement of GAGA factor and Prod from high affin ity sites in euchromatin occurs upon condensation of metaphase chromos omes, Upon decondensation, GAGA factor and Prod shift from low affinit y sites within satellite DNA back to euchromatic sites as a self-assem bly process.