Sorger P K, Murray A W
Department of Microbiology and Immunology, University of California, San Francisco 94143-0502.
Nature. 1992 Jan 23;355(6358):365-8. doi: 10.1038/355365a0.
In somatic cells, entry into mitosis depends on the completion of DNA synthesis. This dependency is established by S-phase feedback controls that arrest cell division when damaged or unreplicated DNA is present. In the fission yeast Schizosaccharomyces pombe, mutations that interfere with the phosphorylation of tyrosine 15 (Y15) of p34cdc2, the protein kinase subunit of maturation promoting factor, accelerate the entry into mitosis and abolish the ability of unreplicated DNA to arrest cells in G2. Because the tyrosine phosphorylation of p34cdc2 is conserved in S. pombe, Xenopus, chicken and human cells, the regulation of p34cdc2-Y15 phosphorylation could be a universal mechanism mediating the S-phase feedback control and regulating the initiation of mitosis. We have investigated these phenomena in the budding yeast Saccharomyces cerevisiae. We report here that the CDC28 gene product (the S. cerevisiae homologue of cdc2) is phosphorylated on the equivalent tyrosine (Y19) during S phase but that mutations that prevent tyrosine phosphorylation do not lead to premature mitosis and do not abolish feedback controls. We have therefore demonstrated a mechanism that does not involve tyrosine phosphorylation of p34 by which cells arrest their division in response to the presence of unreplicated or damaged DNA. We speculate that this mechanism may not involve the inactivation of p34 catalytic activity.
在体细胞中，进入有丝分裂取决于DNA合成的完成。这种依赖性是由S期反馈控制建立的，当存在受损或未复制的DNA时，该控制会阻止细胞分裂。在裂殖酵母粟酒裂殖酵母中，干扰成熟促进因子的蛋白激酶亚基p34cdc2的酪氨酸15（Y15）磷酸化的突变会加速进入有丝分裂，并消除未复制的DNA将细胞阻滞在G2期的能力。由于p34cdc2的酪氨酸磷酸化在粟酒裂殖酵母、非洲爪蟾、鸡和人类细胞中是保守的，p34cdc2-Y15磷酸化的调节可能是介导S期反馈控制和调节有丝分裂起始的普遍机制。我们在芽殖酵母酿酒酵母中研究了这些现象。我们在此报告，CDC28基因产物（cdc2在酿酒酵母中的同源物）在S期期间在等效酪氨酸（Y19）上被磷酸化，但阻止酪氨酸磷酸化的突变不会导致过早有丝分裂，也不会消除反馈控制。因此，我们证明了一种不涉及p34酪氨酸磷酸化的机制，通过该机制细胞会因未复制或受损DNA的存在而阻止其分裂。我们推测这种机制可能不涉及p34催化活性的失活。
