Structural and functional characterization of a Dictyostelium gene encoding a DIF inducible, prestalk-enriched mRNA sequence.

The pDd56 mRNA sequence is highly enriched in prestalk over prespore cells and is inducible by DIF, the putative Dictyostelium stalk-specific morphogen. We show that the pDd56 gene is composed of forty one copies of a twenty four amino acid, cysteine rich repeat. This is highly homologus to a repeat which we have previously shown to compose the major fraction of the pDd63 mRNA, another DIF inducible, prestalk-enriched sequence. The predicted pDd56 protein contains a putative signal peptide but does not appear to contain a transmembrane segment. In combination these features suggest it to be an extrinsic protein and we confirm this elsewhere by showing that the pDd56 gene encodes a known, extracellular protein of the stalk. The pDd56 mRNA is dependent upon exogenous DIF for its accumulation. We show that this control is exerted at the transcriptional level and that a restriction fragment containing 1.7Kb of upstream sequence directs temporally-regulated expression of the gene.