Cdc42p, a Rho-related GTP-binding protein, regulates cytoskeletal polarization and rearrangements in eukaryotic cells. In yeast, Gic1p and Gic2p are effectors of Cdc42p involved in actin polarization at bud emergence. Gic2p is expressed in a cell cycle-dependent manner and rapidly disappears shortly after bud emergence concomitant with the activation of the G1 cyclin-dependent kinase Cdc28p-Clnp. Here we have shown that the rapid disappearance of Gic2p results from ubiquitin-dependent proteolysis. Biochemical and genetic evidence demonstrates that degradation of Gic2p required the Skp1-cullin-F-box protein complex (SCF) components Cdc34p, Cdc53p, Skp1p and Grr1p, but not Cdc4p. Phosphorylation of several C-terminal sites of Gic2p served as part of the recognition signal for ubiquitination. In addition, binding of Gic2p to Cdc42p was a prerequisite for degradation, suggesting that specifically the active form of Gic2p is targeted for destruction. Finally, our data indicate that degradation of Gic2p may be part of a mechanism which restricts cytoskeletal polarization in the G1 phase of the cell cycle.

• PMID: 9736614
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Journal Article | Research Support, Non-U.S. Gov't

Authors

Jaquenoud M, Gulli MP, Peter K, Peter M

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