Lobo S M, Ifill S, Hernandez N
Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724.
Nucleic Acids Res. 1990 May 25;18(10):2891-9. doi: 10.1093/nar/18.10.2891.
Although the human U2 and U6 snRNA genes are transcribed by RNA polymerases II and III respectively, their promoters are remarkably similar in structure. Both promoters contain a proximal element and an enhancer region with an octamer motif. The U6 promoter contains in addition an A/T rich region that defines it as an RNA polymerase III promoter. We have examined in further detail the contributions of sequences in the human U2 and U6 promoter regions to transcription by RNA polymerase II and III. We find that although the sequences surrounding the U2 cap site favor RNA polymerase II transcription, their presence cannot suppress a shift to RNA polymerase III specificity upon insertion of the U6 A/T box. In the U6 promoter, the 3' part of the proximal element homology is essential for efficient transcription and is also involved in localizing the start site of transcription. A region downstream of the proximal element homology is required for RNA polymerase II (but not for RNA polymerase III) transcription, both in the U2 promoter and in the U6 promoter. This element may be recognized by an RNA polymerase II transcription factor or by RNA polymerase II itself. The presence of this element in the U6 promoter raises the possibility that the human U6 gene is, under certain circumstances, transcribed by RNA polymerase II.
尽管人类U2和U6小核RNA基因分别由RNA聚合酶II和III转录，但其启动子在结构上非常相似。两种启动子都包含一个近端元件和一个带有八聚体基序的增强子区域。此外，U6启动子含有一个富含A/T的区域，这使其被定义为RNA聚合酶III启动子。我们进一步详细研究了人类U2和U6启动子区域的序列对RNA聚合酶II和III转录的贡献。我们发现，尽管U2帽位点周围的序列有利于RNA聚合酶II转录，但它们的存在并不能抑制在插入U6 A/T框后向RNA聚合酶III特异性的转变。在U6启动子中，近端元件同源性的3'部分对于有效转录至关重要，并且还参与确定转录起始位点。在U2启动子和U6启动子中，近端元件同源性下游的一个区域是RNA聚合酶II（而非RNA聚合酶III）转录所必需的。该元件可能被RNA聚合酶II转录因子或RNA聚合酶II本身识别。U6启动子中存在该元件增加了人类U6基因在某些情况下由RNA聚合酶II转录的可能性。
