Cyclin Stability

The biochemical mechanism of Mos action is not yet established. Mos has been found to phosphorylate cyclin B in vitro, and it is possible that this phosphorylation directly inhibits cyclin B proteolysis (Roy et al., 1990). However, such a direct effect of phosphorylation on cyclin B stability remains to be demonstrated, and it is alternatively possible that Mos inhibits (directly or indirectly) the proteolytic pathway responsible for cyclin B degradation. Mos has recently been found to stimulate mitogen-activated protein kinase (MAP kinase) in Xenopus oocytes,... 

Hunt Because MAPK is active, so this should stabilize cyclin B. 

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... 

Newport I think that was what it was. Cyclin A stabilizes spindles. In this case, with low Cdc2 it was actually going through mitosis a little bit faster than normal, and the spindle itself might not have time to orient properly, or it might rock a bit. This would result in an asymmetric division. 

Coleman, M. L., Marshall, C. J., and Olson, M. F. Ras promotes p21(Wafl/ Cipl) protein stability via a cyclin Dl-imposed block in proteasome-mediated degradation. Embo J 2003,... 

The conical coal injector was replaced with a blunt cyclin-der with a single axial jet so the flame could be stabilized at lower swirl numbers, thereby reducing the centrifugal deposition on the furnace walls. The radiation shield between the combustor and heat exchanger was removed to reduce particle losses further. The increased radiative transfer decreased the wall temperature substantially. The later experiments were also carried out at lower fuel-air equivalence ratios, i.e., (J> = 0.57. The combination of increased heat losses and increased dilution with excess air reduced the maximum wall temperature to 990°C for the experiments reported below. 

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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