Baldwin D N, Linial M L
Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington 98104, USA.
J Virol. 1998 May;72(5):3658-65. doi: 10.1128/JVI.72.5.3658-3665.1998.
Human foamy virus (HFV) is the prototype of the Spumavirus genus of retroviruses. These viruses have a genomic organization close to that of other complex retroviruses but have similarities to hepadnaviruses such as human hepatitis B virus (HBV). Both HFV and HBV express their Pol protein independently of their structural proteins. Retroviruses and hepadnaviruses differ in their requirements for particle assembly and genome packaging. Assembly of retroviral particles containing RNA genomes requires only the Gag structural protein. The Pol protein is not required for capsid assembly, and the Env surface glycoprotein is not required for release of virions from the cell. In contrast, assembly of extracellular HBV particles containing DNA requires core structural protein and polymerase (P protein) for assembly of nucleocapsids and requires surface glycoproteins for release from the cell. We investigated the requirements for synthesis of extracellular HFV particles by constructing mutants with either the pol or env gene deleted. We found that the Pol protein is dispensable for production of extracellular particles containing viral nucleic acid. In the absence of Env, intracellular particles are synthesized but few or no extracellular particles could be detected. Thus, foamy virus assembly is distinct from that of other reverse transcriptase-encoding mammalian viruses.
人类泡沫病毒（HFV）是逆转录病毒泡沫病毒属的原型。这些病毒的基因组结构与其他复杂逆转录病毒相近，但与嗜肝DNA病毒如人类乙型肝炎病毒（HBV）有相似之处。HFV和HBV均独立于其结构蛋白表达其Pol蛋白。逆转录病毒和嗜肝DNA病毒在病毒颗粒组装和基因组包装的需求方面存在差异。含有RNA基因组的逆转录病毒颗粒的组装仅需要Gag结构蛋白。衣壳组装不需要Pol蛋白，并且病毒粒子从细胞中释放也不需要Env表面糖蛋白。相比之下，含有DNA的细胞外HBV颗粒的组装需要核心结构蛋白和聚合酶（P蛋白）来组装核衣壳，并且需要表面糖蛋白从细胞中释放。我们通过构建缺失pol或env基因的突变体来研究细胞外HFV颗粒合成的需求。我们发现，Pol蛋白对于产生含有病毒核酸的细胞外颗粒是可有可无的。在没有Env的情况下，会合成细胞内颗粒，但几乎检测不到或无法检测到细胞外颗粒。因此，泡沫病毒的组装与其他编码逆转录酶的哺乳动物病毒不同。
