Genetic and biochemical evaluation of the importance of Cdc6 in regulating mitotic exit.
We evaluated the hypothesis that the N-terminal region of the replication control protein Cdc6 acts as an inhibitor of cyclin-dependent kinase (Cdk) activity, promoting mitotic exit. Cdc6 accumulation is restricted to the period from mid-cell cycle until the succeeding G1, due to proteolytic control that requires the Cdc6 N-terminal region. During late mitosis, Cdc6 is present at levels comparable with Sic1 and binds specifically to the mitotic cyclin Clb2. Moderate overexpression of Cdc6 promotes viability of CLB2Deltadb strains, which otherwise arrest at mitotic exit, and rescue is dependent on the N-terminal putative Cdk-inhibitory domain. These observations support the potential for Cdc6 to inhibit Clb2-Cdk, thus promoting mitotic exit. Consistent with this idea, we observed a cytokinesis defect in cdh1Delta sic1Delta cdc6Delta2-49 triple mutants. However, we were able to construct viable strains, in three different backgrounds, containing neither SIC1 nor the Cdc6 Cdk-inhibitory domain, in contradiction to previous work. We conclude, therefore, that although both Cdc6 and Sic1 have the potential to facilitate mitotic exit by inhibiting Clb2-Cdk, mitotic exit nevertheless does not require any identified stoichiometric inhibitor of Cdk activity.
Archambault
Vincent
V
The Rockefeller University, New York, New York 10021, USA.
Li
Caihong X
CX
Tackett
Alan J
AJ
Wasch
Ralph
R
Chait
Brian T
BT
Rout
Michael P
MP
Cross
Frederick R
FR
D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002470:Cell Survival / Q000235:genetics / Q000502:physiology; D019926:Cyclin B; D050756:Cyclin-Dependent Kinase Inhibitor Proteins; D013058:Mass Spectrometry; D008938:Mitosis; D011485:Protein Binding; D017434:Protein Structure, Tertiary / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*
C066503:CDC6 protein, S cerevisiae; C093749:CLB2 protein, S cerevisiae; D018797:Cell Cycle Proteins; D019926:Cyclin B; D050756:Cyclin-Dependent Kinase Inhibitor Proteins; C086926:SIC1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins