Abstract：
Several covalent modifications are found associated with the transcriptionally active chromatin regions constituted by the genes transcribed by RNA polymerase (pol) II. Pol III-transcribed genes code for the small, stable RNA species, which participate in many cellular processes, essential for survival. Pol III transcription is repressed under most of the stress conditions by its negative regulator Maf1. We found that most of the histone acetylations increase with starvation-induced repression on several genes transcribed by the yeast pol III. On one of these genes, SNR6 (coding for the U6snRNA), a strongly positioned nucleosome in the gene upstream region plays regulatory role under repression. On this nucleosome, the changes in H3K9 and H3K14 acetylations show different dynamics. During repression, acetylation levels on H3K9 show steady increase whereas H3K14 acetylation increases with a peak at 40 min after which levels reduce. Both the levels settle by 2 hr to a level higher than the active state, which revert to normal levels with nutrient repletion. The increase in H3 acetylations is seen in the mutants reported to show reduced SNR6 transcription but not in the maf1Δ cells. This increase on a regulatory nucleosome may be part of the signaling mechanisms, which prepare cells for the stress-related quick repression as well as reactivation. The contrasting association of the histone acetylations with pol II and pol III transcription may be an important consideration to make in research studies focused on drug developments targeting histone modifications.
摘要：
发现几种共价修饰与由RNA聚合酶（pol）II转录的基因构成的转录活性染色质区域相关。PolIII转录的基因编码小的，稳定的RNA种类，参与许多细胞过程，对生存至关重要。PolIII转录在大多数胁迫条件下被其负调节因子Maf1抑制。我们发现，大多数组蛋白乙酰化随着饥饿诱导的对酵母polIII转录的几个基因的抑制而增加。在其中一个基因上，SNR6（编码U6snRNA），位于基因上游区域的核小体在抑制下发挥调节作用。在这个核小体上，H3K9和H3K14乙酰化的变化表现出不同的动力学。在镇压期间,H3K9上的乙酰化水平显示稳定增加,而H3K14乙酰化增加,在40分钟时达到峰值,之后水平降低。两个级别都在2小时后稳定到高于活动状态的级别，随着营养补充恢复到正常水平。在据报道显示SNR6转录降低的突变体中观察到H3乙酰化的增加，但在maf1Δ细胞中没有。调节核小体的这种增加可能是信号机制的一部分，为与压力相关的快速抑制和再激活准备细胞。组蛋白乙酰化与polII和polIII转录的对比关联可能是针对组蛋白修饰的药物开发的研究中的重要考虑因素。
