Schepetilnikov Mikhail, Schott Gregory, Katsarou Konstantina, Thiébeauld Odon, Keller Mario, Ryabova Lyubov A
Institut de Biologie Moléculaire des Plantes du CNRS, Université de Strasbourg, 12 rue du Général Zimmer, 67084 Strasbourg Cedex, France.
Nucleic Acids Res. 2009 Sep;37(17):5838-47. doi: 10.1093/nar/gkp609. Epub 2009 Jul 28.
The prototype foamy virus (PFV) is a nonpathogenic retrovirus that shows promise as a vector for gene transfer. The PFV (pre)genomic RNA starts with a long complex leader that can be folded into an elongated hairpin, suggesting an alternative strategy to cap-dependent linear scanning for translation initiation of the downstream GAG open reading frame (ORF). We found that the PFV leader carries several short ORFs (sORFs), with the three 5'-proximal sORFs located upstream of a structural element. Scanning-inhibitory hairpin insertion analysis suggested a ribosomal shunt mechanism, whereby ribosomes start scanning at the leader 5'-end and initiate at the downstream ORF via bypass of the central leader regions, which are inhibitory for scanning. We show that the efficiency of shunting depends strongly on the stability of the structural element located downstream of either sORFs A/A' or sORF B, and on the translation event at the corresponding 5'-proximal sORF. The PFV shunting strategy mirrors that of Cauliflower mosaic virus in plants; however, in mammals shunting can operate in the presence of a less stable structural element, although it is greatly improved by increasing the number of base pairings. At least one shunt configuration was found in primate FV (pre)genomic RNAs.
原型泡沫病毒（PFV）是一种无致病性的逆转录病毒，有望成为基因转移载体。PFV前基因组RNA起始于一个长而复杂的前导序列，该序列可折叠成一个细长的发夹结构，这提示了一种不同于帽依赖性线性扫描的策略，用于下游GAG开放阅读框（ORF）的翻译起始。我们发现PFV前导序列携带几个短ORF（sORF），其中三个5'近端sORF位于一个结构元件的上游。扫描抑制性发夹插入分析提示了一种核糖体跳跃机制，即核糖体从前导序列5'端开始扫描，并通过绕过对扫描有抑制作用的中央前导序列区域，在下游ORF处起始翻译。我们表明，跳跃效率强烈依赖于位于sORF A/A'或sORF B下游的结构元件的稳定性，以及相应5'近端sORF处的翻译事件。PFV的跳跃策略与植物中的花椰菜花叶病毒相似；然而，在哺乳动物中，跳跃可以在结构元件稳定性较低的情况下发生，尽管通过增加碱基配对数量可大大提高跳跃效率。在灵长类泡沫病毒前基因组RNA中发现了至少一种跳跃构型。
