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 multicellular development. At the slug stage cudA is expressed in the prespore cells 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 sub-region. The promoter domain that directs prespore-specific transcription consists of a positively acting region, that has the potential to direct expression in all cells within the slug, and a negatively acting region that prevents expression in the prestalk cells. is the protein that regulates commitment to stalk cell gene expression, where it is known to function as a transcriptional repressor. We show that Dd-duanyu1813a binds in vitro to the positively acting part of the prespore domain of the cudA promoter. However, Dd-duanyu1813a cannot be utilised for this purpose in vivo, because analysis of a Dd-duanyu1813a null mutant strain shows that Dd-duanyu1813a is not necessary for cudA transcription in prespore cells. In contrast, the part of the cudA promoter that directs prestalk-specific expression contains a binding site for Dd-duanyu1813a that is essential for its biological activity. Dd-duanyu1813a 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-duanyu1813a is utilised to activate cudA transcription in prespore cells.

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