Krieg P A, Melton D A
Nature. 1984;308(5955):203-6. doi: 10.1038/308203a0.
The specific 3' termini of a number of eukaryotic mRNAs have been shown to be generated by the post-transcriptional processing of primary transcripts or pre-mRNAs. The sequence AAUAAA, present in the 3' region of nearly all eukaryotic mRNAs, appears to be involved in the cleavage and subsequent polyadenylation of the primary transcript. An exception to this general rule is the case of the histone mRNAs, which lack the AAUAAA sequence and are not normally polyadenylated. Histone mRNAs do, however, contain a highly conserved 23 base pair sequence at their 3' termini, which is required for correct 3' end formation. The similarity between this conserved sequence, which can be drawn as a hairpin loop, and bacterial transcription terminators has led several investigators to suggest that the specific 3' end of histone mRNA is formed by termination of transcription. So far, however, experimental results have not been presented which make it possible to distinguish between a post-transcriptional processing or a transcription termination mechanism for the formation of histone mRNA 3' termini. We have investigated this issue by synthesizing in vitro unprocessed histone pre-mRNAs that extend past the normal 3' terminus. These in vitro synthesized pre-mRNAS were injected into frog oocyte nuclei to study their fate. The results demonstrate that correct 3' ends of chicken histone H2B mRNAs can be formed by RNA processing of longer synthetic pre-mRNAs.
许多真核生物mRNA的特定3'末端已被证明是由初级转录本或前体mRNA的转录后加工产生的。几乎所有真核生物mRNA的3'区域中存在的序列AAUAAA，似乎参与了初级转录本的切割和随后的多聚腺苷酸化。这一普遍规则的一个例外是组蛋白mRNA的情况，它们缺乏AAUAAA序列，通常也不会进行多聚腺苷酸化。然而，组蛋白mRNA在其3'末端确实含有一个高度保守的23个碱基对的序列，这是正确形成3'末端所必需的。这个保守序列可以画成一个发夹环，它与细菌转录终止子之间的相似性使得一些研究人员认为组蛋白mRNA的特定3'末端是由转录终止形成的。然而，到目前为止，尚未有实验结果能够区分组蛋白mRNA 3'末端形成的转录后加工机制或转录终止机制。我们通过在体外合成延伸超过正常3'末端的未加工组蛋白前体mRNA来研究这个问题。将这些体外合成的前体mRNA注射到蛙卵母细胞核中以研究它们的命运。结果表明，较长的合成前体mRNA的RNA加工可以形成鸡组蛋白H2B mRNA的正确3'末端。
