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Molecular and Cellular Biology, October 1999, p. 6929-6939, Vol. 19, No. 10
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

The Morphogenesis Checkpoint in Saccharomyces cerevisiae: Cell Cycle Control of Swe1p Degradation by Hsl1p and Hsl7p

John N. McMillan,1 Mark S. Longtine,2 Rey A. L. Sia,1 Chandra L. Theesfeld,1 Elaine S. G. Bardes,1 John R. Pringle,2 and Daniel J. Lew1,*

Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, North Carolina 27710,1 and Biology Department, University of North Carolina, Chapel Hill, North Carolina 275992

Received 7 June 1999/Returned for modification 13 July 1999/Accepted 26 July 1999

In Saccharomyces cerevisiae, the Wee1 family kinase Swe1p is normally stable during G1 and S phases but is unstable during G2 and M phases due to ubiquitination and subsequent degradation. However, perturbations of the actin cytoskeleton lead to a stabilization and accumulation of Swe1p. This response constitutes part of a morphogenesis checkpoint that couples cell cycle progression to proper bud formation, but the basis for the regulation of Swe1p degradation by the morphogenesis checkpoint remains unknown. Previous studies have identified a protein kinase, Hsl1p, and a phylogenetically conserved protein of unknown function, Hsl7p, as putative negative regulators of Swe1p. We report here that Hsl1p and Hsl7p act in concert to target Swe1p for degradation. Both proteins are required for Swe1p degradation during the unperturbed cell cycle, and excess Hsl1p accelerates Swe1p degradation in the G2-M phase. Hsl1p accumulates periodically during the cell cycle and promotes the periodic phosphorylation of Hsl7p. Hsl7p can be detected in a complex with Swe1p in cell lysates, and the overexpression of Hsl7p or Hsl1p produces an effective override of the G2 arrest imposed by the morphogenesis checkpoint. These findings suggest that Hsl1p and Hsl7p interact directly with Swe1p to promote its recognition by the ubiquitination complex, leading ultimately to its destruction.

* Corresponding author. Mailing address: Department of Pharmacology and Cancer Biology, Box 3686, Duke University Medical Center, Durham, NC 27710. Phone: (919) 613-8627. Fax: (919) 613-8642. E-mail: daniel.lew{at}duke.edu.

Molecular and Cellular Biology, October 1999, p. 6929-6939, Vol. 19, No. 10
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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