The cyclin dependent kinases(CDKs) are critical for progression through the cell cycle. The eel1 cycle protein KIPl, or p27, is an inhibitor of many of the CDK/cyclin complexes. Previously, the KIPl protein has been shown to be ubiquitinated in vivo and in vitro experiments have suggested that this modification requires the Cdc34 ubiquitination enzyme. In yeast , substrates of Cdc34 are believed to be phosphorylated by a CDK complex in order to be recognized by the Cdc34 machinery. In order to determine whether a similar mechanism may function in higher cells, we mutated the potential CDK sites in p27 and assayed the mutant proteins for changes in stability. We identified one mutant which was 5 times more stable than wild-type KIP1 protein. This mutant protein retained its ability to bind CDK2 and inhibit CDK2 kinase activity. These results suggest that the KIPl protein may be targeted for degradation only after CDK phosphorylation.
|Original language||English (US)|
|State||Published - Dec 1 1997|
ASJC Scopus subject areas
- Molecular Biology