A GBF-BINDING SITE AND A NOVEL AT ELEMENT DEFINE THE MINIMAL SEQUENCES SUFFICIENT TO DIRECT PRESPORE-SPECIFIC EXPRESSION IN DICTYOSTELIUM-DISCOIDEUM

In order to better understand the molecular mechanisms of cellular dif ferentiation in Dictostelium discoideum, we have identified the minimu m regulatory sequences of the prespore-specific gene SP60/cotC that ar e sufficient to confer cell-type-specific expression on a heterologous promoter. This region includes at least two essential cia-acting elem ents: a novel AT-rich element (or elements) and CAE3. The essential fu nction of the AT element is confirmed through point mutations that dec rease expression below the level of detection. CAE3 is one of three CA -rich elements (CAEs) required for the induction of SP60/cotC during d evelopment or in response to extracellular cyclic AMP. The CAEs have d ifferential affinities for a specific developmentally induced nuclear activity (CAE1 > CAE2 >> CAE3). Were, we identify this activity as e;G -box-binding factor (GBF) and show that in vitro-transcribed and -tran slated GBF binds all three SP60/cotC CAEs in a sequence specific manne r. Previous studies have suggested that GBF mediates the induction of some prestalk genes, and these results demonstrate that it also has a specific role in prespore gene activation.