Novel Cdc42-binding proteins Gic1 and Gic2 control cell polarity in yeast

  1. Jeffrey L. Brown1,3,
  2. Malika Jaquenoud2,
  3. Marie-Pierre Gulli2,
  4. John Chant1, and
  5. Matthias Peter2,4
  1. 1Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts 02138 USA; 2Institut Suisse de Recherches Expérimentales sur le Cancer (ISREC), 1066 Epalinges/VD Switzerland

Abstract

Cdc42p, a Rho-related GTP-binding protein, regulates cytoskeletal polarization and rearrangements in eukaryotic cells, but the effectors mediating this control remain unknown. Through the use of the complete yeast genomic sequence, we have identified two novel Cdc42p targets, Gic1p and Gic2p, which contain consensus Cdc42/Rac interactive–binding (CRIB) domains and bind specifically to Cdc42p–GTP. Gic1p and Gic2p colocalize with Cdc42p as cell polarity is established during the cell cycle and during mating in response to pheromones. Cells deleted for both GIC genes exhibit defects in actin and microtubule polarization similar to those observed incdc42 mutants. Finally, the interaction of the Gic proteins and Cdc42p is essential, as mutations in the CRIB domain of Gic2p that eliminate Cdc42p binding disrupt Gic2p localization and function. Thus, Gic1p and Gic2p define a novel class of Cdc42p targets that are specifically required for cytoskeletal polarization in vivo.

Keywords

Footnotes

  • 3 Present address: Millenium Pharmaceuticals Inc., Cambridge, Massachusetts 02139 USA.

  • 4 Corresponding author.

  • E-MAIL matthias.peter{at}isrec.unil.ch; FAX (41) 21 652-6933.

    • Received July 25, 1997.
    • Accepted September 9, 1997.
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