Partridge J F, Mikesell G E, Breeden L L
Fred Hutchinson Cancer Research Center, Basic Sciences Division, Seattle, Washington 98104, USA.
J Biol Chem. 1997 Apr 4;272(14):9071-7. doi: 10.1074/jbc.272.14.9071.
Two promoter elements have been defined that activate G1/S-specific transcription in Saccharomyces cerevisiae. SCB elements (CACGAAA) are activated by the Swi4-Swi6 complex, and MCB elements (ACGCGTNA) are activated by the Mbp1-Swi6 complex. CLN1 encodes a cyclin which is expressed during this interval, and requires Swi4 and Swi6 for peak transcription, but it has no consensus SCB elements in its promoter. Two SCB-like sequences had been previously noted and suggested to be the functional promoter elements. Our studies indicate that these sequences are unable to activate transcription of a lacZ reporter construct, or to bind Swi4-Swi6 complexes in vitro. However, a cluster of three sequences resembling MCB sequences are active promoter elements, sufficient to confer G1/S-specific transcription to a reporter. These sites are the predominant activation elements in the CLN1 promoter, and despite their resemblance to MCB elements, they bind Swi4-Swi6 complexes in vitro and require Swi4 and Swi6 for their activity in vivo. This indicates that the sequences that promote Swi4/Swi6 binding have not been fully defined, or that there are multiple Swi4- and Swi6-containing complexes with distinct DNA binding specificities. In addition to these novel Swi4/Swi6-binding sites, these studies also show that there must be at least one novel promoter element that can confer G1/S-specific transcription to CLN1, because when all the potential SCB- and MCB-like sequences are eliminated the transcript is still cell cycle regulated.
已确定两种启动子元件可激活酿酒酵母中G1/S特异性转录。SCB元件（CACGAAA）由Swi4-Swi6复合物激活，MCB元件（ACGCGTNA）由Mbp1-Swi6复合物激活。CLN1编码一种在这一时期表达的细胞周期蛋白，其峰值转录需要Swi4和Swi6，但它的启动子中没有共有SCB元件。之前已注意到两个类似SCB的序列，并认为它们是功能性启动子元件。我们的研究表明，这些序列无法激活lacZ报告基因构建体的转录，也不能在体外结合Swi4-Swi6复合物。然而，一组三个类似MCB序列的序列是活跃的启动子元件，足以赋予报告基因G1/S特异性转录。这些位点是CLN1启动子中的主要激活元件，尽管它们与MCB元件相似，但它们在体外结合Swi4-Swi6复合物，并且在体内发挥活性需要Swi4和Swi6。这表明促进Swi4/Swi6结合的序列尚未完全确定，或者存在多种具有不同DNA结合特异性的含Swi4和Swi6的复合物。除了这些新的Swi4/Swi6结合位点外，这些研究还表明，必须至少存在一种新的启动子元件，它可以赋予CLN1 G1/S特异性转录，因为当所有潜在的类似SCB和MCB的序列被消除时，转录本仍然受细胞周期调控。
