EVIDENCE THAT THE RDEA PROTEIN IS A COMPONENT OF A MULTISTEP PHOSPHORELAY MODULATING RATE OF DEVELOPMENT IN DICTYOSTELIUM

We have isolated an insertional mutant of Dictyostelium discoideum tha t aggregated rapidly and formed spores and stalk cells within 14 h of development instead of the normal 24 h. We have shown by parasexual ge netics that the insertion is in the rdeA locus and have cloned the gen e. It encodes a predicted 28 kDa protein (RdeA) that is enriched in ch arged residues and is very hydrophilic. Constructs with the DNA for th e c-Myc epitope or for the green fluorescent protein indicate that Rde A is not compartmentalized. RdeA displays homology around a histidine residue at amino acid 65 with members of the H2 module family of phosp hotransferases that participate in multistep phosphoryl relays. Replac ement of this histidine rendered the protein inactive. The mutant is c omplemented by transformation with the Ypd1 gene of Saccharomyces cere visiae, itself an H2 module protein. We propose that RdeA is part of a multistep phosphorelay system that modulates the rate of development.