Jacquier A, Rosbash M
Proc Natl Acad Sci U S A. 1986 Aug;83(16):5835-9. doi: 10.1073/pnas.83.16.5835.
Two mutant genes, both of which contain an A----C transversion at the absolutely conserved branch point of the yeast "TACTAAC box" (TACTAAC----TACTACC), were constructed and introduced into yeast cells. Splicing and gene expression are almost completely eliminated by this mutation, but a low level (approximately equal to 0.1%) of proper splicing is detectable. Branch point mapping indicates that the mutant branch is formed at the normal location--i.e., to cytidine rather than adenosine. The mutant branch is also a very poor substrate for the HeLa cell debranching enzyme. Although splicing of the mutant transcripts is very poor, the cells contain a high level of mutant intron because these excised introns are remarkably stable. The results imply that the normal branch point is important not only for branch formation and splicing but also for intron turnover.
构建了两个突变基因，它们在酵母“TACTAAC盒”（TACTAAC----TACTACC）绝对保守的分支点处都含有一个A----C颠换，并将其导入酵母细胞。这种突变几乎完全消除了剪接和基因表达，但仍可检测到低水平（约等于0.1%）的正确剪接。分支点定位表明，突变分支在正常位置形成——即连接到胞嘧啶而非腺嘌呤。突变分支也是HeLa细胞去分支酶的非常差的底物。尽管突变转录本的剪接非常差，但细胞中含有高水平的突变内含子，因为这些切除的内含子非常稳定。结果表明，正常分支点不仅对分支形成和剪接很重要，而且对内含子周转也很重要。
