CDK inhibitory proteins
Association with small inhibitory proteins is a universal mechanism of CDK regulation (Sherr and Roberts, 1999), though the CKIs (Cyclin-dependent Kinase Inhibitors) involved are highly divergent between yeasts and metazoans. Three different proteins, p21 Cip1 , p27 Kip1 and p57 Kip2 , form the "CDK inhibitory Protein/Kinase Inhibitor protein" (Cip/Kip) family in mammals. The C. elegans genome encodes two members of this family: CKI-1 and CKI-2 (Feng et al., 1999; Hong et al., 1998). Although both predicted proteins are similarly close in amino-acid sequence to p21 Cip1 and p27 Kip1 , only CKI-1 appears to act generally in cell-cycle control (Boxem and van den Heuvel, 2001; Feng et al., 1999; Fukuyama et al., 2003; Hong et al., 1998). Several results have shown that CKI-1 acts to promote cell-cycle arrest throughout development, analogous to p27 Kip1 in mammals and Dacapo in flies. Absence of cki-1 as a result of the mnDf100 deletion results in embryonic arrest