SPLICE SITE SELECTION, RATE OF SPLICING, AND ALTERNATIVE SPLICING ON NASCENT TRANSCRIPTS
SPLICE SITE SELECTION, RATE OF SPLICING, AND ALTERNATIVE SPLICING ON NASCENT TRANSCRIPTS
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DOI：
10.1101/gad.2.6.754
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发表时间：
1988-06-01
影响因子：
10.5
通讯作者：
OSHEIM, YN
中科院分区：
文献类型：
--
作者：
BEYER, AL;OSHEIM, YN
基于电子显微镜下活性转录基因的超微结构分析，我们提出证据表明，在早期果蝇胚胎基因的新生转录本上，pre-mRNA剪接以合理的频率发生，剪接位点选择通常先于聚腺苷化。观察到的过程细节与体外剪接系统的结果一致，但不同的是，体内剪接的完成速度更快。对于那些共转录去除的内含子，在3”剪接位点合成后启动一系列事件，从48秒内在3”剪接位点形成核糖核蛋白（RNP）颗粒开始，在2分钟内形成内含子环，在3分钟内剪接。该过程的启动与3”剪接位点合成相关，但与5”剪接位点合成、内含子在转录物中的位置以及转录物的年龄或长度无关。在某些情况下，内含子在转录物的5”端被移除，然后在3”端合成内含子，支持转录顺序在剪接位点配对中的可能作用。总的来说，我们的观察结果与剪接位点选择的“先到先服务”原则是一致的，尽管外显子跳跃的一个观察例子表明，在这个一般框架内可以容纳其他剪接可能性。
Based on the ultrastructural analysis of actively transcribing genes seen in electron micrographs, we present evidence that pre-mRNA splicing occurs with a reasonable frequency on the nascent transcripts of early Drosphila embryo genes and that splice site selection may generally precede polyadenylation. The details of the process observed are in agreement with results from in vitro splicing systems but differ in the more rapid completion in vivo splicing. For those introns that are removed cotranscriptionally, a series of events is initiated following 3'' splice site synthesis, beginning with ribonucleoprotein (RNP) particle formation at the 3'' splice site within 48 sec, intron loop formation within 2 min, and splicing within 3 min. The initiation of the process is correlated with 3'' splice site synthesis but is independent of 5'' splice site synthesis, the position of the intron within the transcript, and the age or length of the transcript. In some cases, introns are removed from the 5'' end of a transcript before introns are synthesized at the 3'' end, supporting a possible role for the order of transcription in splice site pairing. In general, our observations are consistent with the ''first-come-first-served'' principle of splice site selection, although an observed example of exon skipping indicates that alternative splicing possibilities can be accommodated within this general framework.