Cyclin guides the way

Article Abstract:

Enzymes recognize substrates through structural complementarity between the substrate and the enzyme's active site while some enzymes make additional contacts with the substrate that enable them to distinguish between proteins. The cyclin-dependent kinases (CPKs) depend for their activity upon the binding of a regulatory subunit called a cyclin to the catalytic subunit that use various ways to guide enzymes to their targets.

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Yeast G1 cyclins are unstable in G1 phase

Article Abstract:

Cell division in most eukaryotes occurs in late G1 phase at the Start event, in the Saccharomyces cerevisiae yeast. The cyclin dependent kinase Cdc28 and three rate limiting activators Cln1, Cln2 and Cln3 trigger Start. Cln proteolyis was thought to be triggered by mitotic cyclins Clb1,2,3 and 4, but it is shown that G1 cyclins are unstable in G1 phase and that Clb-Cdc28 activity is not required for G1 cyclin turnover.

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Role of a ubiquitin-conjugating enzyme in degradation of S- and M-phase cyclins

Article Abstract:

The nuclear ubiquitin-conjugating enzyme, UBC9, is required for the degradation of M-phase (B-type) cyclins in yeast Xenopus oocytes. The degradation is necessary for the exit from mitosis and is mediated by the ubiquitin-dependent proteolytic system. The cell cycle progression is inhibited by the repression of UBC9 production during the early M phase, resulting in the stabilization of the mutants in UBC9.

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