Brown A J, Jones T, Shuttleworth J
Department of Anatomy, Medical School, University of Birmingham, England.
Mol Biol Cell. 1994 Aug;5(8):921-32. doi: 10.1091/mbc.5.8.921.
Threonine 161 phosphorylation of p34cdc2 and its equivalent threonine 160 in p33cdk2 by cdk-activating kinase (CAK) is essential for the activation of these cyclin-dependent kinases. We have studied the expression and associated kinase activity of p40MO15, the catalytic subunit of CAK, during Xenopus oogenesis, meiotic maturation, and early development to understand in more detail how cdk kinases are regulated during these events. We find that p40MO15 is a stable protein with a half-life > 16 h that is accumulated during oogenesis. p40MO15 protein and its associated CAK activity are localized predominantly to the germinal vesicle; however, a small but significant proportion is found in the cytoplasm. The amount of p40MO15 detected in stage VI oocytes remains unchanged through meiotic maturation, fertilization, and early embryogenesis. Significantly, p40MO15 was found to be constitutively active during oogenesis, meiotic maturation, and the rapid mitotic cycles of early development. This suggests that regulation of p34cdc2 and p33cdk2 activity during cell cycle progression does not involve changes in the level or activity of p40MO15/CAK.
周期蛋白依赖性激酶激活激酶（CAK）使p34cdc2的苏氨酸161以及p33cdk2中与之对应的苏氨酸160发生磷酸化，这对于激活这些周期蛋白依赖性激酶至关重要。我们研究了CAK的催化亚基p40MO15在非洲爪蟾卵子发生、减数分裂成熟及早期发育过程中的表达及相关激酶活性，以更详细地了解在这些过程中周期蛋白依赖性激酶是如何被调控的。我们发现p40MO15是一种半衰期大于16小时的稳定蛋白，在卵子发生过程中积累。p40MO15蛋白及其相关的CAK活性主要定位于生发泡；然而，在细胞质中也发现了一小部分但很显著的比例。在VI期卵母细胞中检测到的p40MO15量在减数分裂成熟、受精及早期胚胎发育过程中保持不变。值得注意的是，发现p40MO15在卵子发生、减数分裂成熟及早期发育的快速有丝分裂周期中持续处于激活状态。这表明在细胞周期进程中对p34cdc2和p33cdk2活性的调控并不涉及p40MO15/CAK水平或活性的变化。
