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 differentiation in Dictostelium discoideum, we have identified the minimum regulatory sequences of the prespore-specific gene SP60/cotC that are sufficient to confer cell-type-specific expression on a heterologous promoter. This region includes at least two essential cia-acting elements: a novel AT-rich element (or elements) and CAE3. The essential function of the AT element is confirmed through point mutations that decrease expression below the level of detection. CAE3 is one of three CA-rich elements (CAEs) required for the induction of SP60/cotC during development or in response to extracellular cyclic AMP. The CAEs have differential 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 -translated GBF binds all three SP60/cotC CAEs in a sequence specific manner. 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.