The Cdc42p GTPase Is Involved in a G2/M Morphogenetic Checkpoint Regulating the Apical-Isotropic Switch and Nuclear Division in Yeast*
- From the Department of Microbiology and Molecular Genetics and the Markey Center for Molecular Genetics, University of Vermont, Burlington, Vermont 05405
Abstract
The Cdc42p GTPase is involved in the signal transduction cascades controlling bud emergence and polarized cell growth in S. cerevisiae. Cells expressing thecdc42 V44A effector domain mutant allele displayed morphological defects of highly elongated and multielongated budded cells indicative of a defect in the apical-isotropic switch in bud growth. In addition, these cells contained one, two, or multiple nuclei indicative of a G2/M delay in nuclear division and also a defect in cytokinesis and/or cell separation. Actin and chitin were delocalized, and septin ring structure was aberrant and partially delocalized to the tips of elongated cdc42 V44Acells; however, Cdc42V44Ap localization was normal. Two-hybrid protein analyses showed that the V44A mutation interfered with Cdc42p’s interactions with Cla4p, a p21(Cdc42/Rac)-activated kinase (PAK)-like kinase, and the novel effectors Gic1p and Gic2p, but not with the Ste20p or Skm1p PAK-like kinases, the Bni1p formin, or the Iqg1p IQGAP homolog. Furthermore, the cdc42 V44A morphological defects were suppressed by deletion of the Swe1p cyclin-dependent kinase inhibitory kinase and by overexpression of Cla4p, Ste20p, the Cdc12 septin protein, or the guanine nucleotide exchange factor Cdc24p. In sum, these results suggest that proper Cdc42p function is essential for timely progression through the apical-isotropic switch and G2/M transition and that Cdc42V44Ap differentially interacts with a number of effectors and regulators.
Footnotes
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↵* This work was supported by National Science Foundation Grants MCB-9405972, MCB-9723071, and MCB-9728218 and by the National Institutes of Health, Cancer Biology Training Grant T32-CAO9286-19 (to T. J. R.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵‡ To whom correspondence should be addressed: Dept. of Microbiology and Molecular Genetics, 202 Stafford Hall, University of Vermont, Burlington, VT 05405. Tel.: 802-656-8203; Fax: 802-656-8749.
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↵2 A. Merla and D. I. Johnson, unpublished results.
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↵3 M. M. Sawyer and D. I. Johnson, manuscript in preparation.
- Abbreviations:
- GAP
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GTPase-activating protein
- PCR
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polymerase chain reaction
- GFP
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green fluorescent potein
- PAK
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p21(Cdc42/Rac)-activated kinase
- DAPI
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4′,6-diamidino-2-phenylindole
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- Received February 23, 1999.
- Revision received March 25, 1999.
- The American Society for Biochemistry and Molecular Biology, Inc.
