Alberghina Lilia, Rossi Riccardo L, Querin Lorenzo, Wanke Valeria, Vanoni Marco
Department of Biotechnology and Biosciences, University of Milano-Bicocca, 20126 Milan, Italy.
J Cell Biol. 2004 Nov 8;167(3):433-43. doi: 10.1083/jcb.200405102. Epub 2004 Nov 1.
Saccharomyces cerevisiae must reach a carbon source-modulated critical cell size, protein content per cell at the onset of DNA replication (Ps), in order to enter S phase. Cells grown in glucose are larger than cells grown in ethanol. Here, we show that an increased level of the cyclin-dependent inhibitor Far1 increases cell size, whereas far1 Delta cells start bud emergence and DNA replication at a smaller size than wild type. Cln3 Delta, far1 Delta, and strains overexpressing Far1 do not delay budding during an ethanol glucose shift-up as wild type does. Together, these findings indicate that Cln3 has to overcome Far1 to trigger Cln-Cdc28 activation, which then turns on SBF- and MBF-dependent transcription. We show that a second threshold is required together with the Cln3/Far1 threshold for carbon source modulation of Ps. A new molecular network accounting for the setting of Ps is proposed.
酿酒酵母必须达到由碳源调节的临界细胞大小，即DNA复制开始时每个细胞的蛋白质含量（Ps），才能进入S期。在葡萄糖中生长的细胞比在乙醇中生长的细胞更大。在这里，我们表明细胞周期蛋白依赖性抑制剂Far1水平的增加会增大细胞大小，而缺失far1的细胞在比野生型更小的细胞大小时就开始出芽和DNA复制。与野生型不同，缺失Cln3、缺失far1以及过表达Far1的菌株在乙醇向葡萄糖转换时不会延迟出芽。这些发现共同表明，Cln3必须克服Far1才能触发Cln-Cdc28激活，进而开启依赖SBF和MBF的转录。我们表明，除了Cln3/Far1阈值外，还需要第二个阈值来进行碳源对Ps的调节。我们提出了一个解释Ps设定的新分子网络。
