Department of Biology and Molecular Biology Institute, San Diego State University, San Diego, CA 92182-1030, USA.
Crit Rev Biochem Mol Biol. 2011 Feb;46(1):11-26. doi: 10.3109/10409238.2010.518136. Epub 2010 Oct 6.
The small nuclear RNAs (snRNAs) are an essential class of non-coding RNAs first identified over 30 years ago. Many of the well-characterized snRNAs are involved in RNA processing events. However, it is now evident that other small RNAs, synthesized using similar mechanisms, play important roles at many stages of gene expression. The accurate and efficient control of the expression of snRNA (and related) genes is thus critical for cell survival. All snRNA genes share a very similar promoter structure, and their transcription is dependent upon the same multi-subunit transcription factor, termed the snRNA activating protein complex (SNAPc). Despite those similarities, some snRNA genes are transcribed by RNA polymerase II (Pol II), but others are transcribed by RNA polymerase III (Pol III). Thus snRNA genes provide a unique opportunity to understand how RNA polymerase specificity is determined and how distinct transcription machineries can interact with a common factor. This review will describe efforts taken toward solving those questions by using the fruit fly as a model organism. Drosophila melanogaster SNAPc (DmSNAPc) binds to a proximal sequence element (PSEA) present in both Pol II and Pol III snRNA promoters. Just a few differences in nucleotide sequence in the Pol II and Pol III PSEAs play a major role in determining RNA polymerase specificity. Furthermore, these same nucleotide differences result in alternative conformations of DmSNAPc on Pol II and Pol III snRNA gene promoters. It seems likely that these DNA-induced alternative DmSNAPc conformations are responsible for the differential recruitment of the distinct transcriptional machineries.
小核 RNA（snRNA）是一类重要的非编码 RNA，最早于 30 多年前被发现。许多特征明确的 snRNA 参与 RNA 加工事件。然而，现在很明显，其他使用类似机制合成的小 RNA 在基因表达的许多阶段发挥着重要作用。因此，snRNA（和相关）基因的表达的准确和高效控制对细胞存活至关重要。所有 snRNA 基因都具有非常相似的启动子结构，它们的转录依赖于相同的多亚基转录因子，称为 snRNA 激活蛋白复合物（SNAPc）。尽管存在这些相似性，但一些 snRNA 基因由 RNA 聚合酶 II（Pol II）转录，而另一些则由 RNA 聚合酶 III（Pol III）转录。因此，snRNA 基因提供了一个独特的机会，可以了解 RNA 聚合酶特异性是如何确定的，以及不同的转录机制如何与共同的因子相互作用。这篇综述将描述使用果蝇作为模型生物来解决这些问题的努力。果蝇 SNAPc（DmSNAPc）与存在于 Pol II 和 Pol III snRNA 启动子中的近端序列元件（PSEA）结合。Pol II 和 Pol III PSEA 中核苷酸序列的几个差异在确定 RNA 聚合酶特异性方面起着主要作用。此外，这些相同的核苷酸差异导致 DmSNAPc 在 Pol II 和 Pol III snRNA 基因启动子上的替代构象。似乎这些 DNA 诱导的替代 DmSNAPc 构象负责募集不同的转录机制。
