Rott R, Drager R G, Stern D B, Schuster G
Department of Biology, Technion-Israel Institute of Technology, Haifa, Israel.
Mol Gen Genet. 1996 Oct 28;252(6):676-83. doi: 10.1007/BF02173973.
A general characteristic of the 3' untranslated regions of plastid mRNAs is an inverted repeat sequence that can fold into a stem-loop structure. These stem-loops are superficially similar to structures involved in prokaryotic transcription termination, but were found instead to serve as RNA 3' end processing signals in spinach chloroplasts, and in the atpB mRNA of Chlamydomonas reinhardtii chloroplasts. In order to carry out a broad study of the efficiency of the untranslated sequences at the 3' ends of chloroplast genes in Chlamydomonas to function as transcription terminators, we performed in vivo run-on transcription experiments using Chlamydomonas chloroplast transformants in which different 3' ends were inserted into the chloroplast genome between a petD promoter and a reporter gene. The results showed that none of the 3' ends that were tested, in either sense or antisense orientation, prevented readthrough transcription, and thus were not highly efficient transcription terminators. Therefore, we suggest that most or all of the 3' ends of mature mRNAs in Chlamydomonas chloroplasts are formed by 3' end processing of longer precursors.
质体mRNA 3'非翻译区的一个普遍特征是存在一个可折叠成茎环结构的反向重复序列。这些茎环在表面上类似于原核转录终止所涉及的结构，但后来发现它们在菠菜叶绿体以及莱茵衣藻叶绿体的atpB mRNA中作为RNA 3'末端加工信号。为了广泛研究衣藻叶绿体基因3'端非翻译序列作为转录终止子的效率，我们利用衣藻叶绿体转化体进行了体内连续转录实验，在这些转化体中，不同的3'端被插入到叶绿体基因组中petD启动子和报告基因之间。结果表明，所测试的3'端无论是正义方向还是反义方向，均不能阻止通读转录，因此不是高效的转录终止子。所以，我们认为衣藻叶绿体中大多数或所有成熟mRNA的3'端是由较长前体的3'末端加工形成的。
