A G-protein β-subunit is essential for Dictyostelium development

Recent studies have demonstrated that G-protein-linked signal transduction pathways play a significant role in the developmental program of the simple eukaryotic organism Dictyostelium. We have reported previously the isolation of a G-protein β-subunit and present here a more complete analysis of this gene. Low-stringency Southern blots and RFLP mapping studies suggest that the β-subunit is a unique gene found on linkage group II. Its deduced amino acid sequence of 347 residues is ∼60% identical to those of the human, Drosophila, and Caenorhabditis elegans β-subunits. The carboxy-terminal 300 residues are about 70% identical; the amino-terminal 50 residues are quite divergent, containing only 10 identities. At all stages of growth and development, a single 1.9-kb β-subunit mRNA is present at a high level, and a specific antibody detects a single 37-kD protein. We propose that G-protein heterotrimers are formed when this β-subunit couples with each of the eight distinct G-protein α-subunits that are transiently expressed during development. Targeted disruption of the β-subunit gene had no effect on the viability of haploid cells, but resulted in the inability of cells to aggregate.