Brady G, Frey J, Danbara H, Timmis K N
J Bacteriol. 1983 Apr;154(1):429-36. doi: 10.1128/jb.154.1.429-436.1983.
Nine high copy number mutations of plasmid R6-5, representing five phenotypically distinct groups, have been identified by DNA sequencing. In each mutant plasmid examined, a single nucleotide change was found. The effects of the mutations on possible gene products, and DNA-RNA secondary structure, were analyzed and compared with the observed phenotypes. The results of this study exclude the possibility that the primary plasmid replication control element, the product of the copA gene, is a polypeptide, and they are consistent with a model of plasmid replication control by the copA product which has the following features: (i) RNA-I, a short untranslated RNA molecule, is the product of the copA gene and regulates the frequency of initiation of plasmid replication, (ii) the hexanucleotide single-strand loop of the major hairpin of RNA-I is its active site, (iii) this active site functions by base pair interactions with its "target," its DNA template strand, or its complementary sequence on RNA-II, a transcript of opposite polarity that is the message of the repA gene, and (iv) the sequence and size of the loop, and the stability of the stem of the hairpin, are all critical factors that govern the functioning of RNA-I.
通过DNA测序已鉴定出质粒R6 - 5的9个高拷贝数突变，它们代表5个表型不同的组。在每个检测的突变体质粒中，均发现了单个核苷酸变化。分析了这些突变对可能的基因产物以及DNA - RNA二级结构的影响，并与观察到的表型进行了比较。本研究结果排除了质粒复制主要控制元件（copA基因的产物）是一种多肽的可能性，并且与copA产物对质粒复制进行控制的模型一致，该模型具有以下特征：（i）RNA - I，一种短的非翻译RNA分子，是copA基因的产物，可调节质粒复制起始频率；（ii）RNA - I主要发夹结构的六核苷酸单链环是其活性位点；（iii）该活性位点通过与它的“靶标”（其DNA模板链或RNA - II上的互补序列）进行碱基对相互作用来发挥功能，RNA - II是极性相反的转录本，是repA基因的信使；（iv）环的序列和大小以及发夹结构茎的稳定性都是决定RNA - I功能的关键因素。
