Martín-Castellanos C, Blanco M A, de Prada J M, Moreno S
Instituto de Microbiología Bioquímica, Departamento de Microbiología y Genética, Consejo Superior de Investigaciones Científicas/Universidad de Salamanca, 37007 Salamanca, Spain.
Mol Biol Cell. 2000 Feb;11(2):543-54. doi: 10.1091/mbc.11.2.543.
Eukaryotic cells coordinate cell size with cell division by regulating the length of the G1 and G2 phases of the cell cycle. In fission yeast, the length of the G1 phase depends on a precise balance between levels of positive (cig1, cig2, puc1, and cdc13 cyclins) and negative (rum1 and ste9-APC) regulators of cdc2. Early in G1, cyclin proteolysis and rum1 inhibition keep the cdc2/cyclin complexes inactive. At the end of G1, the balance is reversed and cdc2/cyclin activity down-regulates both rum1 and the cyclin-degrading activity of the APC. Here we present data showing that the puc1 cyclin, a close relative of the Cln cyclins in budding yeast, plays an important role in regulating the length of G1. Fission yeast cells lacking cig1 and cig2 have a cell cycle distribution similar to that of wild-type cells, with a short G1 and a long G2. However, when the puc1(+) gene is deleted in this genetic background, the length of G1 is extended and these cells undergo S phase with a greater cell size than wild-type cells. This G1 delay is completely abolished in cells lacking rum1. Cdc2/puc1 function may be important to down-regulate the rum1 Cdk inhibitor at the end of G1.
真核细胞通过调节细胞周期G1期和G2期的长度来协调细胞大小与细胞分裂。在裂殖酵母中，G1期的长度取决于细胞周期蛋白依赖性激酶2（Cdc2）的正调控因子（Cig1、Cig2、Puc1和Cdc13细胞周期蛋白）和负调控因子（Rum1和Ste9-后期促进复合体）水平之间的精确平衡。在G1早期，细胞周期蛋白的蛋白水解作用和Rum1的抑制作用使Cdc2/细胞周期蛋白复合物保持无活性。在G1期末期，这种平衡发生逆转，Cdc2/细胞周期蛋白的活性下调Rum1以及后期促进复合体的细胞周期蛋白降解活性。在此，我们展示的数据表明，Puc1细胞周期蛋白（芽殖酵母中Cln细胞周期蛋白的近亲）在调节G1期长度中发挥重要作用。缺乏Cig1和Cig2的裂殖酵母细胞具有与野生型细胞相似的细胞周期分布，G1期短而G2期长。然而，在此遗传背景下缺失puc1(+)基因时，G1期长度延长，这些细胞进入S期时的细胞大小比野生型细胞更大。在缺乏Rum1的细胞中，这种G1期延迟完全消除。Cdc2/Puc1的功能可能对在G1期末期下调Rum1细胞周期蛋白依赖性激酶抑制剂很重要。
