Greenwood E, Nishitani H, Nurse P
Cell Cycle Laboratory, Imperial Cancer Research Fund, London, WC2A 3PX, UK.
J Cell Sci. 1998 Oct;111 ( Pt 20):3101-8. doi: 10.1242/jcs.111.20.3101.
The DNA replication checkpoint is required to maintain the integrity of the genome, inhibiting mitosis until S phase has been successfully completed. The checkpoint preventing premature mitosis in Schizosaccharomyces pombe relies on phosphorylation of the tyrosine-15 residue on cdc2p to prevent its activation and hence mitosis. The cdc18 gene is essential for both generating the DNA replication checkpoint and the initiation of S phase, thus providing a key role for the overall control and coordination of the cell cycle. We show that the C terminus of the protein is capable of both initiating DNA replication and the checkpoint function of cdc18p. The C terminus of cdc18p acts upstream of the DNA replication checkpoint genes rad1, rad3, rad9, rad17, hus1 and cut5 and requires the wee1p/mik1p tyrosine kinases to block mitosis. The N terminus of cdc18p can also block mitosis but does so in the absence of the DNA replication checkpoint genes and the wee1p/mik1p kinases therefore acting downstream of these genes. Because the N terminus of cdc18p associates with cdc2p in vivo, we suggest that by binding the cdc2p/cdc13p mitotic kinase directly, it exerts an effect independently of the normal checkpoint control, probably in an unphysiological manner.
DNA复制检查点对于维持基因组的完整性是必需的，它会抑制有丝分裂，直到S期成功完成。裂殖酵母中防止过早有丝分裂的检查点依赖于cdc2p上酪氨酸-15残基的磷酸化，以防止其激活从而防止有丝分裂。cdc18基因对于产生DNA复制检查点和启动S期都至关重要，因此在细胞周期的整体控制和协调中发挥关键作用。我们表明，该蛋白的C末端能够启动DNA复制和发挥cdc18p的检查点功能。cdc18p的C末端在DNA复制检查点基因rad1、rad3、rad9、rad17、hus1和cut5的上游起作用，并且需要wee1p/mik1p酪氨酸激酶来阻断有丝分裂。cdc18p的N末端也可以阻断有丝分裂，但在没有DNA复制检查点基因和wee1p/mik1p激酶的情况下如此，因此在这些基因的下游起作用。因为cdc18p的N末端在体内与cdc2p结合，我们认为通过直接结合cdc2p/cdc13p有丝分裂激酶，它以一种可能非生理性的方式独立于正常的检查点控制发挥作用。
