title: Regulation of cell polarity by interactions of Msb3 and Msb4 with Cdc42 and polarisome components.
abstract: In Saccharomyces cerevisiae, polarized growth depends on interactions between the actin cytoskeleton and the secretory machinery. Here we show that the Rab GTPase-activating proteins (GAPs) Msb3 and Msb4 interact directly with Spa2, a scaffold protein of the "polarisome" that also interacts with the formin Bni1. Spa2 is required for the polarized localization of Msb3 and Msb4 at the bud tip. We also show that Msb3 and Msb4 bind specifically to Cdc42-GDP and Rho1-GDP in vitro and that Msb3 and Rho GDP dissociation inhibitor act independently but oppositely on Cdc42. Finally, we show that Msb3 and Msb4 are involved in Bni1-nucleated actin assembly in vivo. These results suggest that Msb3 and Msb4 regulate polarized growth by multiple mechanisms, directly regulating exocytosis through their GAP activity toward Sec4 and potentially coordinating the functions of Cdc42, Rho1, and Bni1 in the polarisome through their binding to these GTPases. A functional equivalent of the polarisome probably exists in other fungi and mammals.
authors.affiliation: Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, 421 Curie Blvd., Room 1012, BRB II/III, Philadelphia, PA 19104-6058, USA.
authors.forename: Serguei E
authors.initials: SE
authors.lastname: Tcheperegine
authors.forename: Xiang-Dong
authors.initials: XD
authors.lastname: Gao
authors.forename: Erfei
authors.initials: E
authors.lastname: Bi
mesh_terms: D000199:Actins / Q000737:chemistry / Q000378:metabolism; D002453:Cell Cycle; D002465:Cell Movement; D016764:Cell Polarity; D005089:Exocytosis; D020558:GTP Phosphohydrolases / Q000737:chemistry; D020690:GTPase-Activating Proteins / Q000378:metabolism*; D005838:Genotype; D005982:Glutathione Transferase / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006153:Guanosine Diphosphate / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D008562:Membrane Glycoproteins / Q000378:metabolism; D008840:Microfilament Proteins / Q000378:metabolism; D008857:Microscopy, Interference; D008954:Models, Biological; D008957:Models, Genetic; D005810:Multigene Family; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D013696:Temperature; D020798:Two-Hybrid System Techniques; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism*
chemical_list: D000199:Actins; C419588:BUD8 protein, S cerevisiae; C105191:Bni1 protein, S cerevisiae; D020690:GTPase-Activating Proteins; D047908:Intracellular Signaling Peptides and Proteins; C076360:MSB2 protein, S cerevisiae; C540987:MSB3 protein, S cerevisiae; C540988:MSB4 protein, S cerevisiae; D008562:Membrane Glycoproteins; D008840:Microfilament Proteins; D029701:Saccharomyces cerevisiae Proteins; D006153:Guanosine Diphosphate; D049452:Green Fluorescent Proteins; D005982:Glutathione Transferase; D020558:GTP Phosphohydrolases; D020764:cdc42 GTP-Binding Protein