Rho GTPase regulation of exocytosis in yeast is independent of GTP hydrolysis and polarization of the exocyst complex.
Rho GTPases are important regulators of polarity in eukaryotic cells. In yeast they are involved in regulating the docking and fusion of secretory vesicles with the cell surface. Our analysis of a Rho3 mutant that is unable to interact with the Exo70 subunit of the exocyst reveals a normal polarization of the exocyst complex as well as other polarity markers. We also find that there is no redundancy between the Rho3-Exo70 and Rho1-Sec3 pathways in the localization of the exocyst. This suggests that Rho3 and Cdc42 act to polarize exocytosis by activating the exocytic machinery at the membrane without the need to first recruit it to sites of polarized growth. Consistent with this model, we find that the ability of Rho3 and Cdc42 to hydrolyze GTP is not required for their role in secretion. Moreover, our analysis of the Sec3 subunit of the exocyst suggests that polarization of the exocyst may be a consequence rather than a cause of polarized exocytosis.
Roumanie
Olivier
O
Department of Cell and Developmental Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
Wu
Hao
H
Molk
Jeffrey N
JN
Rossi
Guendalina
G
Bloom
Kerry
K
Brennwald
Patrick
P
D015415:Biomarkers / Q000378:metabolism; D016764:Cell Polarity; D005089:Exocytosis; D036681:Fluorescence Recovery After Photobleaching; D006160:Guanosine Triphosphate / Q000378:metabolism*; D006868:Hydrolysis; D008954:Models, Biological; D050505:Mutant Proteins / Q000378:metabolism; D009154:Mutation; D021122:Protein Subunits / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000201:enzymology* / Q000254:growth & development; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D013696:Temperature; D033921:Vesicular Transport Proteins; D020846:cdc42 GTP-Binding Protein, Saccharomyces cerevisiae / Q000378:metabolism*; D020741:rho GTP-Binding Proteins / Q000378:metabolism*
D015415:Biomarkers; C103132:EXO70 protein, S cerevisiae; D050505:Mutant Proteins; D021122:Protein Subunits; D011993:Recombinant Fusion Proteins; C103130:SEC3 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D033921:Vesicular Transport Proteins; D006160:Guanosine Triphosphate; C074647:RHO3 protein, S cerevisiae; D020846:cdc42 GTP-Binding Protein, Saccharomyces cerevisiae; D020741:rho GTP-Binding Proteins