Hernandez N, Weiner A M
Cell. 1986 Oct 24;47(2):249-58. doi: 10.1016/0092-8674(86)90447-2.
U1 and U2 snRNAs are thought to be transcribed by RNA polymerase II. A conserved sequence known as the 3' box is located just downstream from the snRNA coding region and directs formation of the 3' end of pre-U1 and pre-U2 snRNA. We show here that a U1 or U2 promoter containing an intact snRNA enhancer is required for the U1 3' box to function efficiently. Promoters for genes encoding mRNAs cannot substitute for the snRNA promoter. Thus snRNAs must be transcribed by a specialized transcription complex that differs from transcription complexes synthesizing mRNAs. Moreover, in contrast to polyadenylated and nonpolyadenylated mRNAs, the 3' ends of pre-snRNAs must be generated either by termination of transcription, or by an RNA processing event intimately coupled to transcription.
U1和U2小核RNA（snRNA）被认为是由RNA聚合酶II转录的。一个被称为3'框的保守序列位于snRNA编码区的下游，指导前体U1和前体U2 snRNA 3'端的形成。我们在此表明，U1 3'框要有效发挥功能，需要一个含有完整snRNA增强子的U1或U2启动子。编码mRNA的基因的启动子不能替代snRNA启动子。因此，snRNA必须由一种不同于合成mRNA的转录复合体的特殊转录复合体转录。此外，与多聚腺苷酸化和非多聚腺苷酸化的mRNA不同，前体snRNA的3'端必须通过转录终止或与转录紧密偶联的RNA加工事件产生。
