Role of Suc1 in the activation of the cyclosome by protein kinase Cdk1/cyclin B.
A large complex, called the cyclosome or anaphase-promoting complex, has specific and regulated protein-ubiquitin ligase activity that targets mitotic regulators (such as cyclin B) for degradation at the end of mitosis. In early embryonic cell cycles the cyclosome is inactive in the interphase, but is subsequently converted by protein kinase Cdk1/cyclin B to an active, phosphorylated form, in a process that includes an initial lag period. This time lag may be important to prevent premature self-inactivation of Cdk1/cyclin B before the end of mitosis. We have previously observed that the phosphorylated form of the cyclosome binds to Suc1, a protein that associates with Cdk1 and with phosphate-containing compounds. We now report that low, physiological concentrations of Suc1 stimulate the activation of the interphase form of the cyclosome by the protein kinase. When Suc1 was present from the beginning of the incubation together with protein kinase Cdk1/cyclin B, activation of the cyclosome took place with the normal lag kinetics. However, when interphase cyclosome was first incubated with protein kinase Cdk1/cyclin B without Suc1, the subsequent addition of Suc1 caused a rapid burst of cyclosome activation and the lag was completely abolished. These findings are consistent with the interpretation that following initial slow phosphorylations of the cyclosome by the protein kinase, Suc1 accelerates multiple phosphorylations that culminate in the full activation of the cyclosome. In support of this interpretation, we find that Suc1 stimulates the phosphorylation of several proteins in the preparation of interphase cyclosome and that the effect of Suc1 on phosphorylation was augmented by prior incubation of interphase cyclosome with protein kinase Cdk1/cyclin B.
Shteinberg
M
M
Unit of Biochemistry, The B. Rappaport Faculty of Medicine and The Rappaport Institute for Research in the Medical Sciences, Technion-Israel Institute of Technology, Haifa, 31096, Israel.
Hershko
A
A
D000255:Adenosine Triphosphate / Q000378:metabolism; D064173:Anaphase-Promoting Complex-Cyclosome; D016203:CDC2 Protein Kinase / Q000378:metabolism*; D002384:Catalysis / Q000187:drug effects; D018797:Cell Cycle Proteins; D019926:Cyclin B / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D005656:Fungal Proteins / Q000378:metabolism* / Q000494:pharmacology; D006657:Histones / Q000378:metabolism; D007399:Interphase; D007700:Kinetics; D008025:Ligases / Q000378:metabolism*; D008970:Molecular Weight; D010766:Phosphorylation / Q000187:drug effects; D011506:Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D029702:Schizosaccharomyces pombe Proteins; D019311:Staurosporine / Q000494:pharmacology; D013997:Time Factors; D043743:Ubiquitin-Protein Ligase Complexes; D044767:Ubiquitin-Protein Ligases
D018797:Cell Cycle Proteins; D019926:Cyclin B; D005656:Fungal Proteins; D006657:Histones; D011506:Proteins; D029702:Schizosaccharomyces pombe Proteins; C051655:Suc1 protein, S pombe; D000255:Adenosine Triphosphate; D043743:Ubiquitin-Protein Ligase Complexes; D064173:Anaphase-Promoting Complex-Cyclosome; D044767:Ubiquitin-Protein Ligases; D016203:CDC2 Protein Kinase; D008025:Ligases; D019311:Staurosporine