Prototype Foamy Virus Protease Activity Is Essential for Intraparticle Reverse Transcription Initiation but Not Absolutely Required for Uncoating upon Host Cell Entry
Prototype Foamy Virus Protease Activity Is Essential for Intraparticle Reverse Transcription Initiation but Not Absolutely Required for Uncoating upon Host Cell Entry
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DOI：
10.1128/jvi.02323-12
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发表时间：
2013-03-01
影响因子：
5.4
通讯作者：
Lindemann, Dirk
中科院分区：
文献类型：
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作者：
Huetter, Sylvia;Muellers, Erik;Lindemann, Dirk
泡沫病毒（FVs）在逆转录病毒中是独特的，其在复制后期进行基因组逆转录（RTr），导致感染性DNA基因组，并且还具有不寻常的Pol生物合成和聚合策略。此外，FV在颗粒形态发生和分解期间仅显示非常有限的病毒蛋白酶（PR）的Gag和Pol加工，这两者被认为对病毒感染性至关重要。在这里，我们报告的一代功能原型FV（PFV）颗粒从成熟或部分加工的病毒衣壳和酶蛋白的感染性水平高达20%的野生型。对由不同Gag和Pol组合（包括表达优化的和真实的PFV开放阅读框[ORF]）产生的病毒体的蛋白质和核酸组成以及感染性的分析揭示，在颗粒组装期间Gag而不是Pol的前体加工对于感染性病毒体的产生是必需的。令人惊讶的是，当在病毒生产过程中将加工的Gag（而不是Gag前体）与PR缺陷型Pol前体一起提供时，即使当使用不同的载体或前病毒表达系统时，也获得了感染性的含病毒DNA的颗粒。尽管病毒粒子感染性相对于相应亲本构建体的感染性降低至0.5%至2%，但这一发现推翻了FV文献中的当前教条，即病毒PR活性在靶细胞进入期间的某个点是绝对必要的。此外，它表明，在颗粒组装过程中，病毒PR介导的Gag前体加工启动了颗粒内RTr。最后，它表明逆转录酶（RT）和整合酶在病毒衣壳内的Pol前体中具有酶促活性，从而能够进行生产性宿主细胞感染。
Foamy viruses (FVs) are unique among retroviruses in performing genome reverse transcription (RTr) late in replication, resulting in an infectious DNA genome, and also in their unusual Pol biosynthesis and encapsidation strategy. In addition, FVs display only very limited Gag and Pol processing by the viral protease (PR) during particle morphogenesis and disassembly, both thought to be crucial for viral infectivity. Here, we report the generation of functional prototype FV (PFV) particles from mature or partially processed viral capsid and enzymatic proteins with infectivity levels of up to 20% of the wild type. Analysis of protein and nucleic acid composition, as well as infectivity, of virions generated from different Gag and Pol combinations (including both expression-optimized and authentic PFV open reading frames [ORFs]) revealed that precursor processing of Gag, but not Pol, during particle assembly is essential for production of infectious virions. Surprisingly, when processed Gag (instead of Gag precursor) was provided together with PR-deficient Pol precursor during virus production, infectious, viral DNA-containing particles were obtained, even when different vector or proviral expression systems were used. Although virion infectivity was reduced to 0.5 to 2% relative to that of the respective parental constructs, this finding overturns the current dogma in the FV literature that viral PR activity is absolutely essential at some point during target cell entry. Furthermore, it demonstrates that viral PR-mediated Gag precursor processing during particle assembly initiates intraparticle RTr. Finally, it shows that reverse transcriptase (RT) and integrase are enzymatically active in the Pol precursor within the viral capsid, thus enabling productive host cell infection.