Multifunctional molecular switch essential for cell morphogenesis

细胞增殖期间细胞周期事件的协调部分地通过监视系统来实现。芽殖酵母Saccharomyces cerevisiae的细胞周期进程受到限制性调控，细胞周期中的一些事件受到检测点的调控，这些检测点监测DNA损伤、DNA复制、纺锤体的完整性、纺锤体定位和细胞形态发生。目前还不清楚是否所有的检查点控制已经确定。在这里，我们发现了一个新的检查点存在耦合细胞壁重塑与纺锤体形成。1，3-β-葡聚糖合成酶活性缺陷的fks 1突变体不能形成成熟芽。令人惊讶的是，这些细胞被复制后DNA捕获，但Clb 2 p水平很低，并且没有形成双极纺锤体。我们发现，wac 1（壁检查点缺陷）突变，废除这种逮捕引起的积累Clb 2 p和CLB 2 mRNA，并导致形成双极纺锤体，尽管葡聚糖合成扰动。这些结果表明存在一种新的检查点机制来协调进入有丝分裂，并表明Wac 1 p需要通过CLB 2的转录调节来实现这种检查点功能。此外，我们发现WAC 1与ARP 1（肌动蛋白相关蛋白）相同。Arp 1 p、Nip 100 p和Jnm 1 p是dynactin复合物的组成部分，它们是实现G2期阻滞同时保持细胞高度活力所必需的。这些结果表明，dynactin复合物在新的检查点中具有调节作用，以监测细胞壁的合成。

The coordination of cell cycle events during cell proliferation is attained, in part, through surveillance systems. In the budding yeast Saccharomyces cerevisiae, cell cycle progression is restrictively regulated and some events during cell cycle are regulated by the checkpoints monitoring DNA damage, DNA replication, integrity of the spindle, spindle positioning and cell morphogenesis. It still remained unclear whether all of the checkpoint controls have been identified.Here we found that a novel checkpoint exists to couple cell wall remodeling with spindle formation. fks1 mutants defective in 1,3-β-glucan synthase activity failed to form a mature bud. Surprisingly, these cells arrested with post-replicative DNA but quite low level of Clb2p, and without forming bipolar spindles. We found that wac1 (wall-checkpoint defective) mutation that abolished this arrest caused the accumulation of Clb2p and CLB2 mRNA and leaded to formation of bipolar spindles despite glucan-synthesis perturbation. These results indicate the existence of a novel checkpoint mechanism to coordinate entry into mitosis, and suggest that Wac1p is required to achieve this checkpoint function through a transcriptional regulation of CLB2. Furthermore, we revealed that WAC1 was identical with ARP1 (actin-related protein). Arp1p, Nip100p and Jnm1p, which are components of the dynactin complex, are required to achieve the G2 arrest while keeping cells highly viable. These results indicate that the dynactin complex have a regulatory role in the novel checkpoint to monitor cell wall synthesis.