Gene overexpression through the targeting of transcription activation domains to regulatory DNA via catalytically defective Cas9 (dCas9) represents a powerful approach to investigate gene function as well as the mechanisms of gene control. To date, the most efficient dCas9-based activator is the Synergistic Activation Mediator (SAM) system whereby transcription activation domains are directly fused to dCas9 as well as tethered through MS2 loops engineered into the gRNA. Here, we show that dCas9 fused to the catalytic domain of the histone acetyltransferase CBP is a more potent activator than the SAM system at some loci, but less efficient at other locations in Drosophila cells. Our results suggest that different rate-limiting steps in the transcription cycle are affected by dCas9-CBP and the SAM system, and that comparing these activators may be useful for mechanistic studies of transcription as well as for increasing the number of hits in genome-wide overexpression screens.

中文翻译：

---

dCas9-CBP和SAM系统对基因的激活在靶标偏好上有所不同。

通过经由催化缺陷的Cas9（dCas9）将转录激活域靶向调节性DNA来实现基因的过表达，是研究基因功能以及基因控制机制的有力方法。迄今为止，最有效的基于dCas9的激活剂是协同激活介体（SAM）系统，其中转录激活域直接与dCas9融合，并通过工程化到gRNA的MS2环进行束缚。在这里，我们显示与组蛋白乙酰转移酶CBP的催化结构域融合的dCas9是比SAM系统在某些位点更有效的激活剂，但在果蝇细胞的其他位置效率较低。我们的结果表明，转录周期中不同的限速步骤受dCas9-CBP和SAM系统的影响，