Gligoris Thomas, Thireos George, Tzamarias Dimitris
Institute of Molecular Biology and Biotechnology, Foundation of Research and Technology, University of Crete, P.O. Box 1527, Vassilika Vouton, 711 10 Heraklion, Crete, Greece.
Mol Cell Biol. 2007 Jun;27(11):4198-205. doi: 10.1128/MCB.00238-07. Epub 2007 Mar 26.
The SWR1 complex (SWR1-C)-dependent deposition of the histone variant Htz1 on promoter nucleosomes is typical of Saccharomyces cerevisiae genes whose expression is frequently reprogrammed. Although this epigenetic marking is of significant physiological importance, the determinants of Htz1 deposition, the conditions that set off SWR1-C occupancy, and the implications of Htz1 in transcriptional initiation are issues that remain unresolved. In this report, we addressed these questions by investigating the GAL1 promoter. We show that Htz1 is required for efficient Mediator recruitment and transcription only when the GAL1 promoter is under the influence of the Tup1 corepressor. In fact, we show that it is Tup1 that specifies Htz1 deposition for the promoter nucleosome covering the transcription start site. This deposition occurs rapidly following transcriptional repression, and it correlates with a Tup1-independent transient recruitment of the SWR1 complex. We propose that Tup1 cooperates with SWR1-C and specifies Htz1 deposition at GAL1, thereby marking the promoter for rapid neutralization from its repressive effects.
组蛋白变体Htz1在启动子核小体上的沉积依赖于酿酒酵母中经常重新编程表达的基因的SWR1复合物（SWR1-C）。尽管这种表观遗传标记具有重要的生理意义，但Htz1沉积的决定因素、引发SWR1-C占据的条件以及Htz1在转录起始中的作用仍未解决。在本报告中，我们通过研究GAL1启动子来解决这些问题。我们表明，只有当GAL1启动子受到Tup1共抑制因子的影响时，Htz1才是有效募集中介体和转录所必需的。事实上，我们表明是Tup1指定了覆盖转录起始位点的启动子核小体的Htz1沉积。这种沉积在转录抑制后迅速发生，并且与SWR1复合物的Tup1独立的瞬时募集相关。我们提出Tup1与SWR1-C协同作用，并指定GAL1处的Htz1沉积，从而标记启动子以便迅速消除其抑制作用。
