title: A G-protein beta subunit required for sexual and vegetative development and maintenance of normal G alpha protein levels in Neurospora crassa.
abstract: The genome of the filamentous fungus Neurospora crassa contains a single gene encoding a heterotrimeric G-protein beta subunit, gnb-1. The predicted GNB-1 protein sequence is most identical to G beta proteins from the filamentous fungi Cryphonectria parasitica and Aspergillus nidulans. N. crassa GNB-1 is also 65% identical to the human GNB-1 protein but only 38 and 45% identical to G beta proteins from budding and fission yeasts. Previous studies in animal and fungal systems have elucidated phenotypes of G beta null mutants, but little is known about the effects of G beta loss on G alpha levels. In this study, we analyzed a gnb-1 deletion mutant for cellular phenotypes and levels of the three G alpha proteins. Delta gnb-1 strains are female-sterile, with production of aberrant fertilized reproductive structures. Delta gnb-1 strains conidiate more profusely and have altered mass on solid medium. Loss of gnb-1 leads to inappropriate conidiation and expression of a conidiation-specific gene during growth in submerged culture. Intracellular cyclic AMP levels are reduced by 60% in vegetative plate cultures of delta gnb-1 mutants. Loss of gnb-1 leads to lower levels of the three G alpha proteins under a variety of conditions. Analysis of transcript levels for the gna-1 and gna-2 G alpha genes in submerged cultures indicates that regulation of G alpha protein levels by gnb-1 is posttranscriptional. The results suggest that GNB-1 directly regulates apical extension rate and mass accumulation. In contrast, many other delta gnb-1 phenotypes, including female sterility and defective conidiation, can be explained by altered levels of the three N. crassa G alpha proteins.
authors.affiliation: Department of Microbiology and Molecular Genetics, University of Texas-Houston Medical School, Houston, Texas 77030, USA.
authors.forename: Qi
authors.initials: Q
authors.lastname: Yang
authors.forename: Sheven I
authors.initials: SI
authors.lastname: Poole
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Borkovich
mesh_terms: D000595:Amino Acid Sequence; D000242:Cyclic AMP / Q000378:metabolism; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D018390:Gene Targeting; D005800:Genes, Fungal; D020962:Heterotrimeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D008954:Models, Biological; D008969:Molecular Sequence Data; D009492:Neurospora crassa / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism*; D010641:Phenotype; D012331:RNA, Fungal / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
chemical_list: D005656:Fungal Proteins; D012331:RNA, Fungal; D012333:RNA, Messenger; D000242:Cyclic AMP; D020962:Heterotrimeric GTP-Binding Proteins