Analysis of the promoter of the cudA gene reveals novel mechanisms of Dictyostelium cell type differentiation

The cudA gene encodes a nuclear protein that is essential for normal multic ellular development. At the slug stage cudA is expressed in the prespore ce lls and in a sub-region of the prestalk zone. We show that cap site distal promoter sequences direct cudA expression in prespore cells, while proximal sequences direct expression in the prestalk subregion. The promoter domain that directs prespore-specific transcription consists of a positively acti ng region, that has the potential to direct expression in all cells within the slug, and a negatively acting region that prevents expression in the pr estalk cells. Dd-STATa is the STAT protein that regulates commitment to sta lk cell gene expression, where it is known to function as a transcriptional repressor, We show that Dd-STATa binds in vitro to the positively acting p art of the prespore domain of the cudA promoter. However, Dd-STATa cannot b e utilised for this purpose in vivo, because analysis of a Dd-STATa null mu tant strain shows that Dd-STATa is not necessary for cudA transcription in prespore cells. In contrast, the part of the cudA promoter that directs pre stalk-specific expression contains a binding site for Dd-STATa that is esse ntial for its biological activity. Dd-STATa appears therefore to serve as a direct activator of cudA transcription in prestalk cells, while a protein with a DNA binding specificity highly related to that of Dd-STATa is utilis ed to activate cudA transcription in prespore cells.