Breeden L, Nasmyth K
MRC Laboratory of Molecular Biology, Cambridge, UK.
Nature. 1987;329(6140):651-4. doi: 10.1038/329651a0.
The HO gene of Saccharomyces cerevisiae encodes the endonuclease that initiates mating-type switching. To prevent inopportune switching, HO transcription is restricted to a specific period in the haploid cell cycle, which is just after, and dependent on, the start of the mitotic cell cycle. A repeated promoter element (CACGA4) (refs 7-9) and two trans-acting activators (SWI4 and SWI6) have been identified, which are responsible for the periodic and start-dependent transcription of HO. To understand further the link between start and HO transcription, the SWI6 gene has been cloned and sequenced. The SWI6 protein is similar to the protein in Schizosaccharomyces pombe that is encoded by cdc10 an essential gene specifically required at the start of the cell cycle. The similarity between the SWI6 and cdc10 products, and their common involvement with 'start', suggest that they may share a common mechanism for sensing or executing this critical control step in the cell cycle. The SWI6 and cdc10 proteins also contain two copies of a repeated motif that occurs at least five times in the cytoplasmic domain of the Notch protein of Drosophila melanogaster.
酿酒酵母的HO基因编码启动交配型转换的内切核酸酶。为防止不合时宜的转换，HO转录被限制在单倍体细胞周期的特定时期，即有丝分裂细胞周期开始之后且依赖于该起始。已鉴定出一个重复的启动子元件（CACGA4）（参考文献7 - 9）和两个反式作用激活因子（SWI4和SWI6），它们负责HO的周期性和起始依赖性转录。为进一步了解起始与HO转录之间的联系，已对SWI6基因进行克隆和测序。SWI6蛋白与粟酒裂殖酵母中由cdc10编码的蛋白相似，cdc10是细胞周期开始时特别需要的一个必需基因。SWI6和cdc10产物之间的相似性，以及它们与“起始”的共同关联，表明它们可能共享一种在细胞周期中感知或执行这一关键控制步骤的共同机制。SWI6和cdc10蛋白还包含一个重复基序的两个拷贝，该基序在黑腹果蝇Notch蛋白的细胞质结构域中至少出现五次。
