Stability of Cyclins

In the cell cycle, the different cyclins show characteristic concentration changes in which temporally defined maxima in cyclin concentration are observed (see Fig. 13.7). The changes in cyclin concentration during the cell cycle are initiated by regulated new synthesis and targeted proteolysis. 

The cyclins may be divided into two classes with respect to stability. Tliere are cyclins that are unstable during the whole cell cycle and their concentration is determined in particular by the rate of transcription. In addition, there are cyclins that are only 

Cyclins D and E in mammals are short-hved proteins with a lifetime of only ca. 20 min. Their instability is due to the occurrence of certain sequences in the C-terminal region deletion of these sequences is associated with stabilization of the cyclins (see 13.3.1). These sequence elements are known as PEST sequences, based on their composition. Due to the short half-life, the D type cyclins require a constant stimulus at the transcription level to achieve the concentration in Gi phase necessary for activation of CDK4/6 and to initiate crossing of the restriction point. 

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Winston N J 1997 Stability of cyclin B protein during meiotic maturation and the first mitotic cell division in mouse oocytes. Biol Cell 89 211-219 Winston NJ, Maro B 1995 Calmodulin-dependent protein kinase II is activated transiently in ethanol-stimulated mouse oocytes. Dev Biol 170 350-352 Winston NJ, Bourgain-Guglielmetti F, Ciemerych MA et al 2000 Early development of mouse embryos null mutant for the cyclin A2 gene occurs in the absence of maternally derived cyclin A2 gene products. Dev Biol 223 139-153... 

Casanovas, O., Miro, R, Estanyol, J.M., Itarte, E., Agell, N., and Bachs, O., Osmotic stress regnlates the stability of cyclin D1 in a p38SAPK2-dependent manner, J. Biol. Chem., 275, 35091, 2000. 

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