CELL CYCLE-REGULATED TRANSCRIPTION IN S CEREVISIAE

酿酒酵母HO基因的转录发生在 这取决于细胞周期的开始。 启动子元件CACGAAA (or SCB）和两个反式作用调节剂（SWI4和SWI6） HO转录的细胞周期调控 （Breeden和Nasmyth，1987年a）。这些SCB元素最近被发现 在启动子中有三个G1细胞周期蛋白基因。此外，我们还表明， SWI6是SWI4的周期性表达所必需的，并且需要大量的 含有不同细胞周期调控启动子的DNA合成基因 元件ACGCGTNA（或MCB）。这使我们将SWI6视为一个关键环节， 在G1晚期发生的所有已知的周期性转录事件之间， 并提示SWI6活性的调节可能决定了G1/S 过渡 我们建议继续努力了解裁武条约的机制， 依赖性转录，特别关注合作伙伴， SWI4和SWI6蛋白的活性。我们将寻找依赖启动的 SWI4和SWI6磷酸化的变化。我们还将描述 swi6突变的抑制子，我们已经分离，并确定其他 与SWI6相互作用的基因产物。 我们已经发现，Gl/S特异性转录的一个重要原因是， HO和CLN基因是SWI4转录的细胞周期调控基因。 SWI4启动子中的必需上游激活序列（UAS） 位于140 bp的DNA片段内。这足以维持细胞周期 它包含三个MCB元素。令人惊讶的是，删除所有 三个MCB元件不消除细胞周期调节的转录。 我们建议进一步研究SWI4启动子，以确定新的细胞 周期调节元件140 bp SWI4 UAS也不寻常，因为它 不会激活反向转录。我们建议 筛选负责这种抑制的序列中的突变体， 然后确定该序列是否在其 正常的染色体定位，隔离SWI4启动子从上游 无人机系统。如果是这样的话，我们将获得突变的因素负责这一点， 边界活动。 最后，我们生成了SWI4的稳定的、SWI6独立的形式。 蛋白质，导致高水平的CLN1和CLN2转录整个 细胞周期这对细胞生长具有显著的负面影响。我们提出 来描述这种生长缺陷， 和该表型的高拷贝抑制子。在此过程中，我们将确定 参与G1细胞周期蛋白代谢和活化的其它细胞因子。

Transcription of the S.cerevisiae HO gene occurs immediately after and is dependent upon the Start of the cell cycle. The promoter element CACGAAAA (or SCB) and two trans-acting regulators (SWI4 and SWI6) that are required for the cell cycle regulation of HO transcription have been identified (Breeden and Nasmyth, 1987a). These SCB elements have recently been found in the promoters three Gl cyclin genes. In addition, we have shown that SWI6 is required for the periodic expression of SWI4 and a large group of DNA synthesis genes that contain a different cell cycle regulated promoter element ACGCGTNA (or MCB). This leads us to view SWI6 as a critical link between all the known periodic transcription events that occur in late Gl, and suggests that the regulation of SWI6 activity may define the Gl/S transition. We propose to continue our efforts to understand the mechanisms of Start- dependent tran-scription, with a particular focus on the partners and activities of the SWI4 and SWI6 proteins. We will look for Start-dependent changes in phosphorylation of SWI4 and SWI6. We will also characterize suppressors of swi6 mutations that we have isolated, and identify other gene products that interact with SWI6. We have found that one important cause of Gl/S-specific transcription of HO and the CLN genes is the cell cycle regulation of SWI4 transcription. The essential upstream activation sequence (UAS) in the SWI4 promoter resides within a 140 bp DNA fragment. It is sufficient for cell cycle regulation and contains three MCB elements. Surprisingly, deletion of all three MCB elements does not eliminate cell cycle regulated transcription. We propose further studies of the SWI4 promoter to identify the novel cell cycle regulatory element. The 140 bp SWI4 UAS is also unusual in that it does not activate transcription in the reverse orientation. We propose to screen for mutants in the sequence responsible for this repression and then to determine if this sequence performs a boundary function in its normal chromosomal location, insulating the SWI4 promoter from upstream UAS's. If so, we will obtain mutations in the factors responsible for this boundary activity. Finally, we have generated a stable, SWI6-independent form of the SWI4 protein which causes high level CLN1 and CLN2 transcription throughout the cell cycle. This has a dominant negative effect on cell growth. We propose to characterize this growth defect and to isolate compensatory mutations and high copy suppressors of this phenotype. In so doing, we will identify other cellular factors involved in Gl cyclin metabolism and activation.