Matsumoto J
Department of Chemistry, University of Massachusetts, Amherst 01003.
J Mol Evol. 1994 Dec;39(6):620-4. doi: 10.1007/BF00160407.
Abortive cycling features transcription initiation by RNA polymerase in both prokaryote and eukaryote. It is known that T7 RNA polymerase produces abortive transcripts up to eight ribonucleotides in length depending on the initial sequence of the DNA message. On the other hand, T7 RNA polymerase initiates DNA replication from the T7 primary origin by synthesizing primers. And the shortest primer from the phi l.lB promoter in the primary origin also seems to be eight ribonucleotides in length. Therefore, it is likely that the longest abortive transcript serves as the shortest primer for T7 DNA replication from the primary origin. Considering that promoters often exist in DNA replication origins for example, E. coli oriC and many eukaryotic origins, the early DNA replication system appears to have taken advantage of the abortive cycling of RNA-dependent RNA polymerase that already existed before the emergence of DNA world. The evolutionary primitive RNA polymerase could do both transcription and priming of DNA replication. Accordingly, abortive cycling would play an important role in evolution at the emergence of DNA world. The priming activity of the primitive RNA polymerase would be taken over by primase later, which seems to be a specialized RNA polymerase for abortive cycling.
流产循环的特征是原核生物和真核生物中RNA聚合酶的转录起始。已知T7 RNA聚合酶根据DNA信息的初始序列产生长度达八个核糖核苷酸的流产转录本。另一方面，T7 RNA聚合酶通过合成引物从T7主要起始位点起始DNA复制。并且来自主要起始位点中φ1.1B启动子的最短引物长度似乎也为八个核糖核苷酸。因此，最长的流产转录本很可能作为从主要起始位点进行T7 DNA复制的最短引物。考虑到启动子经常存在于DNA复制起始位点中，例如大肠杆菌oriC和许多真核生物起始位点，早期的DNA复制系统似乎利用了在DNA世界出现之前就已存在的RNA依赖性RNA聚合酶的流产循环。进化上原始的RNA聚合酶可以进行转录和DNA复制的引发。因此，流产循环在DNA世界出现时的进化过程中会发挥重要作用。原始RNA聚合酶的引发活性后来会被引发酶接管，引发酶似乎是一种专门用于流产循环的RNA聚合酶。
