Dalton S, Whitbread L
Roche Institute of Molecular Biology, Nutley, NJ 07110, USA.
Proc Natl Acad Sci U S A. 1995 Mar 28;92(7):2514-8. doi: 10.1073/pnas.92.7.2514.
The CDC47 gene was isolated by complementation of a cdc47 temperature-sensitive mutant in Saccharomyces cerevisiae and was shown to encode a predicted polypeptide, Cdc47, of 845 aa. Cdc47 belongs to the Cdc46/Mcm family of proteins, previously shown to be essential for initiation of DNA replication. Using indirect immunofluorescence microscopy and subcellular fractionation techniques, we show that Cdc47 undergoes cell cycle-regulated changes in its subcellular localization. At mitosis, Cdc47 enters the nucleus, where it remains until soon after the initiation of DNA replication, when it is rapidly exported back into the cytoplasm. Cdc47 protein levels do not vary with the cell cycle, but expression of CDC47 and nascent synthesis of Cdc47 occur late in the cell cycle, coinciding with mitosis. Together, these results show that Cdc47 is not only imported into the nucleus at the end of mitosis but is also exported back into the cytoplasm at the beginning of S phase. The observation that Cdc47 is exported from the nucleus at the beginning of S phase has important implications for how initiation of DNA replication is controlled.
CDC47基因是通过对酿酒酵母中cdc47温度敏感突变体进行互补分离得到的，结果显示它编码一个预测的由845个氨基酸组成的多肽Cdc47。Cdc47属于Cdc46/Mcm蛋白家族，先前已证明该家族对于DNA复制的起始至关重要。利用间接免疫荧光显微镜和亚细胞分级分离技术，我们发现Cdc47在亚细胞定位上经历了细胞周期调控的变化。在有丝分裂时，Cdc47进入细胞核，并一直保持在细胞核内，直到DNA复制开始后不久，此时它会迅速被转运回细胞质中。Cdc47蛋白水平不会随细胞周期而变化，但CDC47的表达和Cdc47的新生合成发生在细胞周期后期，与有丝分裂同时发生。这些结果共同表明，Cdc47不仅在有丝分裂末期被导入细胞核，而且在S期开始时也会被转运回细胞质中。Cdc47在S期开始时从细胞核中输出这一观察结果，对于DNA复制起始的控制方式具有重要意义。
