Lowndes N F, Johnson A L, Breeden L, Johnston L H
Laboratory of Yeast Genetics, National Institute for Medical Research, Mill Hill, London, UK.
Nature. 1992 Jun 11;357(6378):505-8. doi: 10.1038/357505a0.
In budding yeast many genes are expressed under cell-cycle control in late G1. These include a large group of DNA synthesis genes, the HO gene involved in mating-type switching, CTS1 (chitinase) and also CLN1 and CLN2 (ref. 4) encoding G1 cyclins. Two factors, encoded by the SWI4 and SWI6 genes, are required for HO (ref. 5), CLN (refs 6, 7) and CTS1 (ref. 3) gene expression and, at least in the HO promoter, bind to CACGA4 upstream sequences (CCBs). This motif is not found upstream of the DNA synthesis genes, which instead have a hexamer element, ACGCGT1 (MCB), an MluI restriction site, that is recognized by a cell-cycle regulated transcription complex DSC1 (ref. 1). This MluI-activation system consisting of the MCBs and DSC1 is conserved in fission yeast where a DSC1-like complex controls the cdc22+ ribonucleotide reductase gene. The Schizosaccharomyces pombe cdc10+ gene encodes a component of DSC1 (ref. 10) and, significantly, this has homology with both the Swi4 and Swi6 proteins. Here we show that Swi6 is an essential component of DSC1 and that deletion of SWI6 impairs the cell-cycle regulation of the DNA synthesis genes, as well as CLN1 and CLN2. Thus Swi6 is the common factor in regulation of all the above genes and may therefore be responsible for the timing of their expression in late G1.
在出芽酵母中，许多基因在G1晚期受细胞周期调控表达。这些基因包括一大组DNA合成基因、参与交配型转换的HO基因、CTS1（几丁质酶）以及编码G1细胞周期蛋白的CLN1和CLN2（参考文献4）。由SWI4和SWI6基因编码的两个因子是HO（参考文献5）、CLN（参考文献6、7）和CTS1（参考文献3）基因表达所必需的，并且至少在HO启动子中，它们与上游序列CACGA4（CCB）结合。这种基序在DNA合成基因的上游未发现，相反，这些基因具有一个六聚体元件ACGCGT1（MCB），即一个MluI限制位点，它被细胞周期调控的转录复合物DSC1（参考文献1）识别。由MCB和DSC1组成的这种MluI激活系统在裂殖酵母中是保守的，在裂殖酵母中，一个类似DSC1的复合物控制cdc22 + 核糖核苷酸还原酶基因。粟酒裂殖酵母的cdc10 + 基因编码DSC1的一个组分（参考文献10），并且值得注意的是，它与Swi4和Swi6蛋白都具有同源性。在这里我们表明，Swi6是DSC1的一个必需组分，并且SWI6的缺失会损害DNA合成基因以及CLN1和CLN2的细胞周期调控。因此，Swi6是上述所有基因调控中的共同因子，因此可能负责它们在G1晚期表达的时间安排。
