Krol A, Carbon P, Ebel J P, Appel B
Nucleic Acids Res. 1987 Mar 25;15(6):2463-78. doi: 10.1093/nar/15.6.2463.
We have cloned and sequenced a 977bp DNA fragment, pXTU6-2, that represents the transcription unit for a Xenopus tropicalis U6 RNA gene. This basic repeating unit is reiterated ca.500-fold per haploid genome. Oocyte injections of pXTU6-2 led to the transcription of a mature-sized U6 RNA that, however, lacked internal 2'-O-methylations. These posttranscriptional modifications of U6 RNA might be cytoplasmic and could require its association with U4 RNA to be accomplished. The low alpha- amanitin sensitivity of U6 RNA synthesis in oocytes suggested that U6 RNA is transcribed by RNA polymerase III, consistent with features of the U6 RNA molecule which also contains a Box A- like intragenic control region. Inspection of X. tropicalis, mouse and human U6 DNA upstream sequences revealed the presence of a TATA box as well as of the proximal and enhancer (octamer motif) elements contained in snRNA genes transcribed by RNA polymerase II. We propose that U6 RNAs are synthesized by a specialized transcription complex consisting of RNA polymerase III and transcription factors, some of which are very likely shared with RNA polymerase II promoters.
我们克隆并测序了一段977bp的DNA片段pXTU6-2，它代表热带爪蟾U6 RNA基因的转录单元。这个基本重复单元在单倍体基因组中约重复500次。将pXTU6-2注射到卵母细胞中可导致成熟大小的U6 RNA转录，然而，该转录产物缺乏内部2'-O-甲基化修饰。U6 RNA的这些转录后修饰可能发生在细胞质中，并且可能需要与U4 RNA结合才能完成。卵母细胞中U6 RNA合成对α-鹅膏蕈碱的低敏感性表明，U6 RNA是由RNA聚合酶III转录的，这与U6 RNA分子的特征一致，该分子还包含一个类似A框的基因内控制区域。对热带爪蟾、小鼠和人类U6 DNA上游序列的检查发现，存在一个TATA框以及由RNA聚合酶II转录的snRNA基因中所含的近端元件和增强子（八聚体基序）元件。我们提出，U6 RNA由一个由RNA聚合酶III和转录因子组成的特殊转录复合体合成，其中一些转录因子很可能与RNA聚合酶II启动子共享。
