Evidence for splice site pairing via intron definition in Schizosaccharomyces pombe
Evidence for splice site pairing via intron definition in Schizosaccharomyces pombe
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DOI：
10.1128/mcb.20.21.7955-7970.2000
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发表时间：
2000-11-01
影响因子：
5.3
通讯作者：
Wise, JA
中科院分区：
文献类型：
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作者：
Romfo, CM;Alvarez, CJ;Wise, JA
Schizosaccharomyces pombe pre- mrna通常是多内含子的，并且与来自Drosophila melanogaster的pre- mrna具有某些特征，其中初始剪接位点配对可以通过外显子或内含子定义进行。在这里，我们提出了三条证据表明，尽管有这些相似之处，裂变酵母剪接很可能仅限于内含子定义。首先，突变S. pombe cdc2基因内外显子两侧的剪接位点，几乎只产生内含子保留，这与在脊椎动物中观察到的外显子跳变相反。其次，我们无法在裂变酵母cgs2中诱导内部微外显子的跳跃，而在哺乳动物中，默认剪接途径不包括极小的外显子。因为通过扩展微外显子可以实现cgs2中下游内含子的几乎定量去除，我们提出其保留是由于位阻闭塞。第三，裂变酵母cdc2的第二个内含子中的几个隐5'连接位于内含子内，而在后生动物中它们通常位于外显子位置。扩展和收缩内含子的作用与内含子定义所预测的一致；事实上，如果距离3′剪接信号更近，即使高度异常的5′连接也能有效地与标准的5′剪接位点竞争。综上所述，我们的数据表明，S. pombe的剪接位点配对很可能只发生在内含子上，这种方式有利于切除尽可能小的片段。
Schizosaccharomyces pombe pre-mRNAs are generally multi-intronic and share certain features with pre-mRNAs from Drosophila melanogaster, in which initial splice site pairing can occur via either exon or intron definition. Here, we present three lines of evidence suggesting that, despite these similarities, fission yeast splicing is most likely restricted to intron definition. First, mutating either or both splice sites flanking an internal exon in the S. pombe cdc2 gene produced almost exclusively intron retention, in contrast to the exon skipping observed in vertebrates. Second, we were unable to induce skipping of the internal microexon in fission yeast cgs2, whereas the default splicing pathway excludes extremely small exons in mammals, Because nearly quantitative removal of the downstream intron in cgs2 could be achieved by expanding the microexon, we propose that its retention is due to steric occlusion. Third, several cryptic 5' junctions in the second intron of fission yeast cdc2 are located within the intron, in contrast to their generally exonic locations in metazoa. The effects of expanding and contracting this intron are as predicted by intron definition; in fact, even highly deviant 5' junctions can compete effectively with the standard 5' splice site if they are closer to the 3' splicing signals. Taken together, our data suggest that pairing of splice sites in S. pombe most likely occurs exclusively across introns in a manner that favors excision of the smallest segment possible.