Dirksen W P, Sun Q, Rottman F M
Department of Molecular Biology and Microbiology, Case Western Reserve University, School of Medicine, Cleveland, Ohio 44106-4960.
J Biol Chem. 1995 Mar 10;270(10):5346-52. doi: 10.1074/jbc.270.10.5346.
A fraction of bovine growth hormone (bGH) pre-mRNA undergoes alternative splicing in which the last intron is retained and transported to the cytoplasm. Our goal was to characterize the cis-acting signals in bGH pre-mRNA that collectively determine the distribution between intron splicing and intron retention. We now demonstrate that the balance between splicing and intron retention in cytoplasmic mRNA is primarily determined by the interaction of three splicing signals and the degree to which these signals deviate from consensus splicing signals. Intron retention requires the presence of both suboptimal 5'- and 3'-splice sites. Mutation of either splice site toward consensus leads to complete splicing of the intron. In the presence of both wild-type, suboptimal splice sites, efficient splicing of this intron is ensured by the presence of a third splicing element, a purine-rich exonic splicing enhancer (ESE). Although strong ESEs can be contained within very small sequences, the bGH ESE activity appears to be composed of multiple sequences spread throughout a 115-nucleotide region of exon 5. Consequently, the final ratio of splicing to intron retention depends on the balance between the relative strengths of each of these three splicing signals, which still allow intron-containing coding sequences to be transported to the cytoplasm.
一部分牛生长激素（bGH）前体mRNA会发生可变剪接，其中最后一个内含子被保留并转运到细胞质中。我们的目标是鉴定bGH前体mRNA中的顺式作用信号，这些信号共同决定内含子剪接和内含子保留之间的分布。我们现在证明，细胞质mRNA中剪接和内含子保留之间的平衡主要由三个剪接信号的相互作用以及这些信号与共有剪接信号的偏离程度决定。内含子保留需要次优的5'-和3'-剪接位点同时存在。任一剪接位点向共有序列突变都会导致内含子完全剪接。在野生型、次优剪接位点都存在的情况下，第三个剪接元件，即富含嘌呤的外显子剪接增强子（ESE）的存在确保了该内含子的有效剪接。尽管强ESE可以包含在非常小的序列中，但bGH的ESE活性似乎由分布在外显子5的115个核苷酸区域中的多个序列组成。因此，剪接与内含子保留的最终比例取决于这三个剪接信号各自相对强度之间的平衡，这仍然允许含内含子的编码序列转运到细胞质中。
