UMMS Affiliation

Department of Molecular Genetics and Microbiology

Publication Date


Document Type



Alleles; *Cell Polarity; GTP-Binding Protein alpha Subunits; GTP-Binding Protein beta Subunits; GTP-Binding Protein gamma Subunits; Guanosine Triphosphate; Heterotrimeric GTP-Binding Proteins; Hydrolysis; Models, Biological; Mutation; Phenotype; Pheromones; Protein Binding; Receptors, Pheromone; Recombinant Fusion Proteins; Saccharomyces cerevisiae; Saccharomyces cerevisiae Proteins; Signal Transduction; Suppression, Genetic; Tropism


Life Sciences | Medicine and Health Sciences


Saccharomyces cerevisiae mating pheromones trigger dissociation of a heterotrimeric G protein (Galphabetagamma) into Galpha-guanosine triphosphate (GTP) and Gbetagamma. The Gbetagamma dimer regulates both mitogen-activated protein (MAP) kinase cascade signaling and cell polarization. Here, by independently activating the MAP kinase pathway, we studied the polarity role of Gbetagamma in isolation from its signaling role. MAP kinase signaling alone could induce cell asymmetry but not directional growth. Surprisingly, active Gbetagamma, either alone or with Galpha-GTP, could not organize a persistent polarization axis. Instead, following pheromone gradients (chemotropism) or directional growth without pheromone gradients (de novo polarization) required an intact receptor-Galphabetagamma module and GTP hydrolysis by Galpha. Our results indicate that chemoattractant-induced cell polarization requires continuous receptor-Galphabetagamma communication but not modulation of MAP kinase signaling. To explore regulation of Gbetagamma by Galpha, we mutated Gbeta residues in two structurally distinct Galpha-Gbeta binding interfaces. Polarity control was disrupted only by mutations in the N-terminal interface, and not the Switch interface. Incorporation of these mutations into a Gbeta-Galpha fusion protein, which enforces subunit proximity, revealed that Switch interface dissociation regulates signaling, whereas the N-terminal interface may govern receptor-Galphabetagamma coupling. These findings raise the possibility that the Galphabetagamma heterotrimer can function in a partially dissociated state, tethered by the N-terminal interface.

DOI of Published Version



Mol Biol Cell. 2008 Jan;19(1):181-97. Epub 2007 Oct 31. Link to article on publisher's site

Journal/Book/Conference Title

Molecular biology of the cell

Related Resources

Link to Article in PubMed

PubMed ID