He X, Jones M H, Winey M, Sazer S
Verna and Marrs McLean Department of Biochemistry, Baylor College of Medicine, One Baylor Plaza, Houston, Texas 77030, USA.
J Cell Sci. 1998 Jun;111 ( Pt 12):1635-47. doi: 10.1242/jcs.111.12.1635.
The spindle assembly checkpoint pathway is not essential for normal mitosis but ensures accurate nuclear division by blocking the metaphase to anaphase transition in response to a defective spindle. Here, we report the isolation of a new spindle checkpoint gene, mph1 (Mps1p-like pombe homolog), in the fission yeast Schizosaccharomyces pombe, that is required for checkpoint activation in response to spindle defects. mph1 functions upstream of mad2, a previously characterized component of the spindle checkpoint. Overexpression of mph1, like overexpression of mad2, mimics activation of the checkpoint and imposes a metaphase arrest. mph1 protein shares sequence similarity with Mps1p, a dual specificity kinase that functions in the spindle checkpoint of the budding yeast Saccharomyces cerevisiae. Complementation analysis demonstrates that mph1 and Mps1p are functionally related. They differ in that Mps1p, but not mph1, has an additional essential role in spindle pole body duplication. We propose that mph1 is the MPS1 equivalent in the spindle checkpoint pathway but not in the SPB duplication pathway. Overexpression of mad2 does not require mph1 to impose a metaphase arrest, which indicates a mechanism of spindle checkpoint activation other than mph1/Mps1p kinase-dependent phosphorylation. In the same screen which led to the isolation of mad2 and mph1, we also isolated dph1, a cDNA that encodes a protein 46% identical to an S. cerevisiae SPB duplication protein, Dsk2p. Our initial characterization indicates that S.p. dph1 and S.c. DSK2 are functionally similar. Together these results suggest that the budding and fission yeasts share common elements for SPB duplication, despite differences in SPB structure and the timing of SPB duplication relative to mitotic entry.
纺锤体组装检查点通路对于正常有丝分裂并非必不可少，但它通过响应有缺陷的纺锤体而阻断中期到后期的转变来确保精确的核分裂。在此，我们报告了在裂殖酵母粟酒裂殖酵母中分离出一个新的纺锤体检查点基因mph1（Mps1p样粟酒裂殖酵母同源物），它是响应纺锤体缺陷而激活检查点所必需的。mph1在mad2的上游起作用，mad2是纺锤体检查点先前已鉴定的一个组分。mph1的过表达，如同mad2的过表达一样，模拟了检查点的激活并导致中期停滞。mph1蛋白与Mps1p具有序列相似性，Mps1p是一种双特异性激酶，在芽殖酵母酿酒酵母的纺锤体检查点中起作用。互补分析表明mph1和Mps1p在功能上相关。它们的不同之处在于，Mps1p在纺锤极体复制中具有额外的重要作用，而mph1则没有。我们提出，mph1是纺锤体检查点通路中与MPS1等效的基因，但在纺锤极体复制通路中并非如此。mad2的过表达不需要mph1来导致中期停滞，这表明存在一种除mph1/Mps1p激酶依赖性磷酸化之外的纺锤体检查点激活机制。在导致分离出mad2和mph1的同一筛选中，我们还分离出了dph1，这是一个编码与酿酒酵母纺锤极体复制蛋白Dsk2p有46%同一性的蛋白质的cDNA。我们的初步表征表明，粟酒裂殖酵母的dph1和酿酒酵母的DSK2在功能上相似。这些结果共同表明，尽管纺锤极体结构以及相对于有丝分裂进入的纺锤极体复制时间存在差异，但芽殖酵母和裂殖酵母在纺锤极体复制方面具有共同的元件。
