Cloning and targeted mutations of Gα7 and Gα8, two developmentally regulated G protein α-subunit genes in Dictyostelium

GTP-binding protein (G protein)-mediated signal transduction pathways play essential roles during the aggregation and differentiation process of Dictyostelium. In addition to the five known G protein α-subunit genes, we recently identified three novel α-subunit genes, Gα6, Gα7, and Gα8, using the polymerase chain reaction technique. We present here a more complete analysis of Gα7 and Gα8. The cDNAs of these two genes were cloned, and their complete nucleotide sequences were determined. Sequence analyses indicate that Gα8 possesses some unusual features. It lacks the 'TCATDT' motif, a sequence of amino acids highly conserved among Gα subunits, and has an additional 50 amino acids at its C-terminus consisting of long stretches of asparagine. Moreover, Gα8 is unusually resistant to protease digestion, which may indicate a slow GTP hydrolysis rate. The possible functions of these α-subunits were assessed by generating mutants lacking Gα7 or Gα8 by gene targeting through homologous recombination and by overexpressing Gα7 or Gα8 protein. Overexpression of Gα7 resulted in abnormal morphogenesis starting at the slug stage, whereas analysis of the other strains failed to reveal any obvious growth or developmental defects under either normal or stressful conditions. The implications of these results are discussed.