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首页> 外文期刊>Plasmid: An International Journal Devoted to Extrachromosomal Gene Systems >Translation initiation of the replication initiator repB gene of promiscuous plasmid pMV158 is led by an extended non-SD sequence
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Translation initiation of the replication initiator repB gene of promiscuous plasmid pMV158 is led by an extended non-SD sequence

机译：混杂质粒pMV158的复制启动子repB基因的翻译起始是由扩展的非SD序列引起的

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摘要

RepB is the pMV158-encoded protein that initiates rolling-circle replication of this promiscuous plasmid. Availability of RepB is rate-limiting for the plasmid replication process, and therefore the repB gene encoding the protein is subjected to strict control. Two trans-acting plasmid elements, CopG and the antisense RNAII, are involved in controlling the synthesis of the initiator at the transcriptional and translational level, respectively. In addition to this dual control of repB expression that senses and corrects fluctuations in plasmid copy number, proper availability of RepB also relies on the adequate functionality of the transcription and translation initiation regulatory signals. Translation of repB has been postulated to depend on an atypical ribosome binding site that precedes its start codon, although such a hypothesis has never been proved. To define sequences involved in translation of repB, several mutations in the translation initiation region of the repB mRNA have been characterized by using an Escherichia coli in vitro expression system wherein the synthesis of RepB was detected and quantified. We showed that translation of repB is not coupled to that of copG and depends only on its own initiation signals. The atypical ribosome binding site, as it was defined, is not involved in translation initiation. However, the sequence just upstream of the repB start codon, encompassing the proximal box of the atypical ribosome binding site and the four bases immediately downstream of it, is indeed important for efficient translation of repB. The high degree of conservation of this sequence among the rep genes of plasmids of the same pMV158 family supports its relevancy as a translation initiation signal in mRNAs without a recognizable Shine-Dalgarno sequence.
机译：RepB是pMV158编码的蛋白，可启动该混杂质粒的滚环复制。 RepB的可用性限制了质粒复制过程的速率，因此编码该蛋白的repB基因受到严格控制。两种反式作用的质粒元件，CopG和反义RNAII，分别在转录和翻译水平上参与控制启动子的合成。除了感知和纠正质粒拷贝数波动的repB表达的双重控制外，RepB的适当可用性还依赖于转录和翻译起始调控信号的适当功能。 repB的翻译被认为取决于其起始密码子之前的非典型核糖体结合位点，尽管这种假设尚未得到证实。为了定义涉及repB翻译的序列，已经通过使用大肠杆菌体外表达系统表征了repB mRNA的翻译起始区域中的几个突变，其中检测和定量了RepB的合成。我们表明，repB的翻译与copG的翻译不相关，仅取决于其自身的起始信号。如定义的，非典型核糖体结合位点不参与翻译起始。然而，repB起始密码子上游的序列，包括非典型核糖体结合位点的近端盒和紧邻其下游的四个碱基，对于有效翻译repB确实很重要。在同一pMV158家族的质粒的rep基因中，该序列的高度保守性支持了其作为mRNA的翻译起始信号的相关性，而无需识别Shine-Dalgarno序列。

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