Yu Yaxin, Yarrington Robert M, Chuong Edward B, Elde Nels C, Stillman David J
Department of Pathology, University of Utah Health Sciences Center, Salt Lake City, UT 84112;
Department of Human Genetics, University of Utah Health Sciences Center, Salt Lake City, UT 84112.
Proc Natl Acad Sci U S A. 2016 Aug 23;113(34):9575-80. doi: 10.1073/pnas.1601793113. Epub 2016 Aug 9.
The yeast HO endonuclease is expressed in late G1 in haploid mother cells to initiate mating-type interconversion. Cells can be arrested in G1 by nutrient deprivation or by pheromone exposure, but cells that resume cycling after nutrient deprivation or cyclin-dependent kinase (CDK) inactivation express HO in the first cell cycle, whereas HO is not expressed until the second cycle after release from pheromone arrest. Here, we show that transcription of a long noncoding RNA (lncRNA) mediates this differential response. The SBF and Mediator factors remain bound to the inactive promoter during arrest due to CDK inactivation, and these bound factors allow the cell to remember a transcriptional decision made before arrest. If the presence of mating pheromone indicates that this decision is no longer appropriate, a lncRNA originating at -2700 upstream of the HO gene is induced, and the transcription machinery displaces promoter-bound SBF, preventing HO transcription in the subsequent cell cycle. Further, we find that the displaced SBF is blocked from rebinding due to incorporation of its recognition sites within nucleosomes. Expressing the pHO-lncRNA in trans is ineffective, indicating that transcription in cis is required. Factor displacement during lncRNA transcription could be a general mechanism for regulating memory of previous events at promoters.
酵母HO内切核酸酶在单倍体母细胞的G1晚期表达，以启动交配型相互转换。细胞可通过营养剥夺或信息素暴露阻滞在G1期，但在营养剥夺或细胞周期蛋白依赖性激酶（CDK）失活后恢复周期的细胞在第一个细胞周期表达HO，而从信息素阻滞释放后直到第二个周期才表达HO。在此，我们表明长链非编码RNA（lncRNA）的转录介导了这种差异反应。由于CDK失活，SBF和中介因子在阻滞期间仍与无活性启动子结合，这些结合的因子使细胞能够记住阻滞前做出的转录决定。如果交配信息素的存在表明这个决定不再合适，就会诱导一种起源于HO基因上游-2700处的lncRNA，转录机制取代启动子结合的SBF，阻止HO在随后的细胞周期中转录。此外，我们发现由于其识别位点被整合到核小体中，被取代的SBF被阻止重新结合。反式表达pHO-lncRNA无效，表明顺式转录是必需的。lncRNA转录过程中的因子取代可能是一种在启动子处调节对先前事件记忆的普遍机制。
