Genetics, Vol 147, 137-145, Copyright © 1997

INVESTIGATIONS

Overlapping Functions for Two G Protein {alpha} Subunits in Neurospora crassa

R. A. Baasiri, X. Lu, P. S. Rowley, G. E. Turner and K. A. Borkovich
Department of Microbiology and Molecular Genetics, University of Texas-Houston Medical School, Houston, Texas 77030, Department of Plant Pathology and Microbiology, Texas A & M University, College Station, Texas 77843

Heterotrimeric G proteins, consisting of {alpha}, {beta} and {gamma} subunits, mediate a variety of signaling pathways in eukaryotes. We have previously identified two genes, gna-1 and gna-2, that encode G protein {alpha} subunits in the filamentous fungus Neurospora crassa. Mutation of gna-1 results in female infertility and sensitivity to hyperosmotic media. In this study, we investigate the expression and functions of gna-2. Results from Western analysis and measurements of gna-2 promoter-lacZ fusion activity indicate that gna-2 is expressed during the vegetative and sexual cycle of N. crassa in both A and a mating types. Activating mutations predicted to abolish the GTPase activity of GNA-2 cause subtle defects in aerial hyphae formation and conidial germination. Extensive phenotypic analysis of {Delta}gna-2 strains did not reveal abnormalities during vegetative or sexual development. In contrast, deletion of gna-2 in a {Delta}gna-1 strain accentuates the {Delta}gna-1 phenotypes. {Delta}gna-1 {Delta}gna-2 strains have a slower rate of hyphal apical extension than {Delta}gna-1 strains on hyperosmotic media. Moreover, {Delta}gna-1 {Delta}gna-2 mutants have more pronounced defects in female fertility than {Delta}gna-1 strains. We propose that gna-1 and gna-2 have overlapping functions and may constitute a gene family. This is the first report of G protein {alpha} subunits with overlapping functions in eukaryotic microbes.

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