[unreadable] Many genes that respond to developmental cues must maintain their responding states long after the cues disappear. In Drosophila, the maintenance of repressed states of many developmentally important genes is accomplished by a protein called POLYCOMB, and by interacting proteins of the Polycomb Group. Homologous proteins are found in mammals, where they appear to have analogous functions. The long-term repression by the Polycomb Group is accompanied by a change in chromosome structure, making it less accessible to transcription factors and polymerases. [unreadable] The Polycomb Group proteins act through DNA sites called Polycomb Response Elements. The best examples of such sites are in the Drosophila bithorax complex, a cluster of genes that control segmental differentiation. Although one of these sites has been localized to a segment of about 1500 base pairs, it is not yet clear how it regulates the genes of the bithorax complex, because there are no mutations that surgically target this Polycomb Response Element. Our goal is to use gene conversion to generate a series of small deletions in and around this site, and to study the consequences for the genes of the bithorax complex. We hope to learn if the Polycomb Response Element is required for activation as well as repression, how the element receives its initial cue, and whether it is redundant or cooperative with other such elements in the bithorax complex. The deletions may permit a functional subdivision of the element, and further conversion experiments will target binding sites for particular Polycomb Group proteins. A second Polycomb Response Element in the bithorax complex will also be dissected by gene conversion, and its properties compared. [unreadable] This application is for a Fogarty International Research Collaboration Award. The research will be done primarily in Hungary at the Biological Research Center of the Hungarian Academy of Sciences, in collaboration with L[unreadable]szl[unreadable] Sipos, as an extension of NIH grant #R01 GM28630-21. [unreadable] [unreadable] [unreadable]