Cross F R, Hoek M, McKinney J D, Tinkelenberg A H
Rockefeller University, New York, New York 10021.
Mol Cell Biol. 1994 Jul;14(7):4779-87. doi: 10.1128/mcb.14.7.4779-4787.1994.
Expression of the Saccharomyces cerevisiae CLN1 and CLN2 genes is cell cycle regulated, and the genes may be controlled by positive feedback. It has been proposed that positive feedback operates via Cln/Cdc28 activation of the Swi4/Swi6 transcription factor, leading to CLN1 and CLN2 transcription due to Swi4 binding to specific sites (SCBs) in the CLN1 and CLN2 promoters. To test this proposal, we have examined the effects of deletion either of the potential SCBs in the CLN2 promoter or of the SWI4 gene on CLN2 transcriptional control. Deletion of a restriction fragment containing the identified SCBs from the promoter does not prevent cell cycle regulation of CLN2 expression, although expression is lowered at all cell cycle positions. A promoter containing a 5.5-kb plasmid insertion or an independent 2.5-kb insertion at the point of deletion of the SCB-containing restriction fragment also exhibits cell cycle regulation, so involvement of unidentified upstream SCBs is unlikely. Neither Swi4 nor the related Mbp1 transcription factor is required for cell cycle regulation of the intact CLN2 promoter. In contrast, Swi4 (but not Mbp1) is required for correct cell cycle regulation of the insertion/deletion promoter lacking SCB sites. We have extended previous genetic evidence for involvement of Swi4 in some aspect of CLN2 function: a mutant hunt for CLN2 positive regulatory factors yielded only swi4 mutations at saturation. Swi4 may bind to nonconsensus sequences in the CLN2 promoter (possibly in addition to consensus sites), or it may act indirectly to regulate CLN2 expression.
酿酒酵母CLN1和CLN2基因的表达受细胞周期调控，且这些基因可能受正反馈控制。有人提出，正反馈通过Cln/Cdc28对Swi4/Swi6转录因子的激活来发挥作用，由于Swi4与CLN1和CLN2启动子中的特定位点（SCB）结合，从而导致CLN1和CLN2转录。为了验证这一观点，我们研究了CLN2启动子中潜在的SCB缺失或SWI4基因缺失对CLN2转录调控的影响。从启动子中缺失包含已鉴定SCB的限制片段，虽然在所有细胞周期阶段表达都会降低，但并不妨碍CLN2表达的细胞周期调控。在缺失含SCB的限制片段的位点处含有5.5 kb质粒插入或独立2.5 kb插入的启动子也表现出细胞周期调控，因此不太可能涉及未鉴定的上游SCB。完整的CLN2启动子的细胞周期调控既不需要Swi4也不需要相关的Mbp1转录因子。相比之下，对于缺乏SCB位点的插入/缺失启动子的正确细胞周期调控，需要Swi4（而不是Mbp1）。我们扩展了先前关于Swi4参与CLN2功能某些方面的遗传学证据：对CLN2正调控因子的突变筛选在饱和状态下仅产生了swi4突变。Swi4可能与CLN2启动子中的非共有序列结合（可能除了共有位点之外），或者它可能间接作用来调节CLN2的表达。
