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Eukaryotic Cell, June 2002, p. 378-390, Vol. 1, No. 3
1535-9778/02/$04.00+0     DOI: 10.1128/EC.1.3.378-390.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

A G-Protein ß Subunit Required for Sexual and Vegetative Development and Maintenance of Normal G{alpha} Protein Levels in Neurospora crassa

Qi Yang,,{dagger} Sheven I. Poole, and Katherine A. Borkovich*

Department of Microbiology and Molecular Genetics, University of Texas-Houston Medical School, Houston, Texas 77030

Received 19 November 2001/ Accepted 25 March 2002

The genome of the filamentous fungus Neurospora crassa contains a single gene encoding a heterotrimeric G-protein ß subunit, gnb-1. The predicted GNB-1 protein sequence is most identical to Gß 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 Gß proteins from budding and fission yeasts. Previous studies in animal and fungal systems have elucidated phenotypes of Gß null mutants, but little is known about the effects of Gß 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.

* Corresponding author. Present address: Department of Plant Pathology, 2317 Webber Hall, University of California, Riverside, CA 92521. Phone: (909) 787-2753. Fax: (909) 787-4294. E-mail: Katherine.Borkovich{at}ucr.edu.

{dagger} Present address: Department of Pediatrics-Genetics, Baylor College of Medicine, Houston, TX 77030.

Eukaryotic Cell, June 2002, p. 378-390, Vol. 1, No. 3
1535-9778/02/$04.00+0     DOI: 10.1128/EC.1.3.378-390.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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Copyright © 2002 by the American Society for Microbiology.