Yeast U6 snRNA made by RNA polymerase II is less stable but functional.
Yeast U6 snRNA made by RNA polymerase II is less stable but functional.
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DOI：
10.1261/rna.079328.122
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发表时间：
2022-12
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U6小核（sn）RNA是剪接体中最短和最保守的snRNA，并形成其活性位点的实质性部分。与其他四种由RNA聚合酶（RNAP）II合成的剪接体snRNA不同，U6由RNAP III合成。为了确定U6功能的某些方面是否与RNAP II合成不相容，我们创建了具有RNAP II启动子和终止子序列的U6 snRNA基因。这种“U6-II”基因在酵母中作为U6 snRNA的唯一来源起作用，但其转录物的稳定性远低于RNAP III产生的U6 snRNA。在U6-II上加入U4 snRNA Sm蛋白结合位点，可增加其稳定性，并形成U6-II·Sm复合物。我们的结论是合成U6 snRNA RNAP III是不需要其功能和U6 snRNP含有Sm复合物可以在体内形成。用RNAP II合成U6 snRNA的能力放松了由基因内RNAP III启动子和终止子元件施加的序列限制，并允许通过RNAP II转录的调节剂容易地控制U6水平。
U6 small nuclear (sn)RNA is the shortest and most conserved snRNA in the spliceosome and forms a substantial portion of its active site. Unlike the other four spliceosomal snRNAs, which are synthesized by RNA polymerase (RNAP) II, U6 is made by RNAP III. To determine if some aspect of U6 function is incompatible with synthesis by RNAP II, we created a U6 snRNA gene with RNAP II promoter and terminator sequences. This “U6-II” gene is functional as the sole source of U6 snRNA in yeast, but its transcript is much less stable than U6 snRNA made by RNAP III. Addition of the U4 snRNA Sm protein binding site to U6-II increased its stability and led to formation of U6-II•Sm complexes. We conclude that synthesis of U6 snRNA by RNAP III is not required for its function and that U6 snRNPs containing the Sm complex can form in vivo. The ability to synthesize U6 snRNA with RNAP II relaxes sequence restraints imposed by intragenic RNAP III promoter and terminator elements and allows facile control of U6 levels via regulators of RNAP II transcription.