DEVELOPMENTAL SIGNAL-TRANSDUCTION PATHWAYS UNCOVERED BY GENETIC SUPPRESSORS

We have found conditions for saturation mutagenesis by restriction enz yme mediated integration that result In plasmid tagging of disrupted g enes, Using this method we selected for mutations in genes that act at checkpoints downstream of the intercellular signaling system that con trols encapsulation in Dictyostelium discoideum. One of these genes, m kcA, is a member of the mitogen-activating protein kinase cascade fami ly while the other, regA, is a novel bipartite gene homologous to resp onse regulators in one part and to cyclic nucleotide phosphodiesterase s in the other part, Disruption of either of these genes results in pa rtial suppression of the block to spare formation resulting from the l oss of the prestalk genes, tagB and tagC. The products of the tag gene s have conserved domains of serine proteases attached to ATP-driven tr ansporters, suggesting that they process and export peptide signals, T ogether, these genes outline an intercellular communication system tha t coordinates organismal shape with cellular differentiation during de velopment.