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Published November 1996 | Published
Journal Article Open

Interaction between Yeast Cdc6 Protein and B-Type Cyclin/Cdc28 Kinases

Abstract

During purification of recombinant Cdc6 expressed in yeast, we found that Cdc6 interacts with the critical cell cycle, cyclin-dependent protein kinase Cdc28. Cdc6 and Cdc28 can be coimmunoprecipitated from extracts, Cdc6 is retained on the Cdc28-binding matrix p13-agarose, and Cdc28 is retained on an affinity column charged with bacterially produced Cdc6. Cdc6, which is a phosphoprotein in vivo, contains five Cdc28 consensus sites and is a substrate of the Cdc28 kinase in vitro. Cdc6 also inhibits Cdc28 histone H1 kinase activity. Strikingly, Cdc6 interacts preferentially with B-type cyclin/Cdc28 complexes and not Cln/Cdc28 in log-phase cells. However, Cdc6 does not associate with Cdc28 when cells are blocked at the restrictive temperature in a cdc34 mutant, a point in the cell cycle when the B-type cyclin/Cdc28 inhibitor p40Sic1 accumulates and purified p40Sic1 inhibits the Cdc6/Cdc28 interaction. Deletion of the Cdc28 interaction domain from Cdc6 yields a protein that cannot support growth. However, when overproduced, the mutant protein can support growth. Furthermore, whereas overproduction of wild-type Cdc6 leads to growth inhibition and bud hyperpolarization, overproduction of the mutant protein supports growth at normal rates with normal morphology. Thus, the interaction may have a role in the essential function of Cdc6 in initiation and in restraining mitosis until replication is complete.

Additional Information

© 1996 by The American Society for Cell Biology. Under the License and Publishing Agreement, authors grant to the general public, effective two months after publication of (i.e.,. the appearance of) the edited manuscript in an online issue of MBoC, the nonexclusive right to copy, distribute, or display the manuscript subject to the terms of the Creative Commons–Noncommercial–Share Alike 3.0 Unported license (http://creativecommons.org/licenses/by-nc-sa/3.0). Submitted March 19, 1996; Accepted August 23, 1996. Monitoring Editor: David Botstein. We are grateful to William Dunphy, Thomas Coleman, and Raymond Deshaies for helpful discussions, strains, and critique of this manuscript. This work was supported by National Institutes of Health grants GM-25508 and GM-47281 to J.L.C. and GM-48492 to A.J.

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