French R, Ahlquist P
Institute for Molecular Virology, University of Wisconsin-Madison 53706.
J Virol. 1988 Jul;62(7):2411-20. doi: 10.1128/JVI.62.7.2411-2420.1988.
Expression of brome mosaic virus (BMV) coat protein and internal genes of many other positive-strand RNA viruses requires initiation of subgenomic mRNA synthesis from specific internal sites on minus-strand genomic RNA templates. Biologically active viral cDNA clones were used to investigate the sequences controlling production of BMV subgenomic RNA in vivo. Suitable duplications directed production of specifically initiated, capped subgenomic RNAs from new sites in the BMV genome. Previously implicated promoter sequences extending 20 bases upstream (-20) and 16 bases downstream (+16) of the subgenomic RNA initiation site directed only low-level synthesis. Subgenomic RNA production at normal levels required sequences extending to at least -74 but not beyond -95. Loss of an (rA)18 tract immediately upstream of the -20 to +16 "core promoter" particularly inhibited subgenomic RNA synthesis. The -38 to -95 region required for normal initiation levels contains repeats of sequence elements in the core promoter, and duplications creating additional upstream copies of these repeats stimulated subgenomic RNA synthesis above wild-type levels. At least four different subgenomic RNAs can be produced from a single BMV RNA3 derivative. For all derivatives producing more than one subgenomic RNA, a gradient of accumulation progressively favoring smaller subgenomic RNAs was seen.
雀麦花叶病毒（BMV）外壳蛋白以及许多其他正链RNA病毒内部基因的表达，需要从负链基因组RNA模板上的特定内部位点起始亚基因组mRNA的合成。具有生物活性的病毒cDNA克隆被用于研究在体内控制BMV亚基因组RNA产生的序列。合适的重复序列可指导从BMV基因组新位点产生特异性起始的、带帽的亚基因组RNA。先前认为的位于亚基因组RNA起始位点上游20个碱基（-20）和下游16个碱基（+16）的启动子序列仅指导低水平合成。正常水平的亚基因组RNA产生需要延伸至至少-74但不超过-95的序列。在-20至+16“核心启动子”紧邻上游的（rA）18序列的缺失尤其抑制亚基因组RNA的合成。正常起始水平所需的-38至-95区域包含核心启动子中序列元件的重复，并且产生这些重复的额外上游拷贝的重复序列刺激亚基因组RNA合成超过野生型水平。从单个BMV RNA3衍生物中可产生至少四种不同的亚基因组RNA。对于所有产生不止一种亚基因组RNA的衍生物，观察到一种逐渐有利于较小亚基因组RNA积累的梯度。
