Hannon G E, Hannon G J, Maroney P A, Nilsen T W
Department of Molecular Biology and Microbiology, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106.
J Biol Chem. 1994 Apr 29;269(17):12387-90.
We have used block-substitution mutagenesis and in vitro transcription assays to identify cis-acting DNA sequence elements important for initiation and 3'-end formation of a U1 small nuclear RNA (snRNA) in the parasitic nematode Ascaris lumbricoides. Efficient initiation of synthesis by RNA polymerase II requires a compact element centered approximately 50 base pairs upstream of the transcriptional start site. Surprisingly, 3'-end formation of U1 snRNAs synthesized in vitro is solely dependent upon elements within the U1 coding sequence. In all other systems studied thus far, 3'-end formation of U snRNAs requires signals present in the 3'-flanking region. We also show that sequence elements that direct 3'-end formation of the A. lumbricoides trans-spliced leader RNA function when RNA synthesis is initiated from the U1 promoter. These results indicate that 3'-end formation of U snRNAs in nematodes is mechanistically distinct from the analogous process in higher eukaryotes.
我们利用块替代诱变和体外转录分析，来鉴定对寄生线虫蛔虫中U1小核RNA（snRNA）的起始和3'端形成至关重要的顺式作用DNA序列元件。RNA聚合酶II高效起始合成需要一个紧密元件，该元件位于转录起始位点上游约50个碱基对处。令人惊讶的是，体外合成的U1 snRNAs的3'端形成仅取决于U1编码序列内的元件。在迄今为止研究的所有其他系统中，U snRNAs的3'端形成需要3'侧翼区域中存在的信号。我们还表明，当从U1启动子起始RNA合成时，指导蛔虫反式剪接前导RNA 3'端形成的序列元件起作用。这些结果表明，线虫中U snRNAs的3'端形成在机制上与高等真核生物中的类似过程不同。
