Westin G, Lund E, Murphy J T, Pettersson U, Dahlberg J E
EMBO J. 1984 Dec 20;3(13):3295-301. doi: 10.1002/j.1460-2075.1984.tb02293.x.
We have analyzed the requirements for human U2 RNA transcription by injection of cloned U2/6 RNA genes into nuclei of Xenopus laevis oocytes. Two forms of human U2 RNAs accumulate, a major species corresponding to mature-sized U2 RNA and a minor species corresponding to a 3'-extended precursor. This RNA polymerase II transcription requires only 258 and 94 bp of 5'- and 3'-flanking region sequences, respectively. Efficient U2 RNA synthesis depends on a promoter element located between positions -258 and -198. This region contains a 12-bp direct repeat which strongly resembles a comparable upstream promoter element of the human U1 RNA genes. Sequences between -258 and -198 also confer on the U2 RNA template the ability to complete with co-injected U1 RNA templates for a snRNA gene-specific transcription factor(s). Transcription of U2 RNA is reduced off templates containing an active RNA polymerase III transcription unit, presumably because of relaxation or sequestration of the DNA. In vitro transcription of the U2 RNA gene, like that of the U1 RNA gene, is initiated upstream of the point corresponding to the 5' end of in vivo synthesized RNA.
我们通过将克隆的U2/6 RNA基因注射到非洲爪蟾卵母细胞核中来分析人类U2 RNA转录的需求。积累了两种形式的人类U2 RNA，一种主要形式对应于成熟大小的U2 RNA，另一种次要形式对应于3'延伸的前体。这种RNA聚合酶II转录分别仅需要258和94 bp的5'和3'侧翼区域序列。高效的U2 RNA合成取决于位于-258和-198位置之间的启动子元件。该区域包含一个12 bp的直接重复序列，与人类U1 RNA基因的类似上游启动子元件非常相似。-258和-198之间的序列还赋予U2 RNA模板与共注射的U1 RNA模板竞争snRNA基因特异性转录因子的能力。U2 RNA的转录在含有活性RNA聚合酶III转录单元的模板上减少，可能是由于DNA的松弛或隔离。U2 RNA基因的体外转录，与U1 RNA基因一样，在对应于体内合成RNA 5'端的点上游起始。
