Processing of Intronless Pre-mRNAs

The 3' ends of eukaryotic mRNAs are generated by posttranscriptional processing of an extended primary transcript. For almost all RNAs, 3' processing consists of two steps: The mRNA is first cleaved at a particular phosphodiester bond downstream of the coding sequence. The upstream fragment then receives a poly(A) tail of approximately 250 adenylate residues whereas the downstream fragment is degraded. The two partial reactions are coupled so that reaction intermediates are usually undetectable. While 3' processing can be studied as an isolated event in vitro, it appears to be connected to transcription, splicing and transcription termination in vivo.

真核生物mRNA的3'端通过初级转录本的转录后加工而产生。对于几乎所有RNA而言，3'端加工包括两个步骤：首先，mRNA在编码序列下游的特定磷酸二酯键处被切割。上游片段随后接上一个由大约250个腺苷酸残基组成的Poly(A)尾巴，而下游片段则被降解。这两个部分反应相互耦合，使得反应中间产物通常难以检测。尽管在体外可以将3'端加工作为一个独立的事件进行研究，但在体内，它似乎与转录、剪接和转录终止紧密相连。