Loewy A, Smyth J, von Bonsdorff C H, Liljeström P, Schlesinger M J
Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri 63110.
J Virol. 1995 Jan;69(1):469-75. doi: 10.1128/JVI.69.1.469-475.1995.
Alphavirus genomes encode a small hydrophobic protein of 6 kDa (the 6K protein) that is expressed as part of a large polyprotein containing the sequences of the two virus transmembranal glycoproteins which form the spikes of the infectious particle. Although made in amounts equivalent to those of the glycoproteins, very little of the 6K protein is found in secreted infectious virions. The role of this protein in virus replication and structure has been studied by use of a variety of mutationally altered forms of 6K, which yield phenotypically distinct viruses. A complete deletion of the gene encoding the 6K protein (delta 6K) of Semliki Forest Virus (SFV) has been constructed from an SFV infectious cDNA and the transcribed RNA-produced progeny virus that closely resembled the normal virus (P. Liljeström, S. Lusa, D. Huylebroeck, and H. Garoff, J. Virol. 65:4107-4113, 1991). Further studies of this mutant have now been performed, and they show that growth of delta 6K has a strong dependency on its host cell, varying from 2 to 50% of the rate of formation of the wild-type SFV. Mammalian cells are much more defective than insect and avian cells in replication of the delta 6K mutant. This mutant is not defective in formation and transport of the glycoproteins or in production of nucleocapsids, which accumulate at the plasma cell membrane in infected BHK cells. The major defect, thus, is in the final assembly and budding of new virus. In BHK cells infected with the delta 6K strain, a relatively large fraction of the total infectious virus formed can be recovered by osmotic lysis of exhaustively washed cells. Infectious SFV totally lacking 6K is identical to wild-type SFV in the early stages of virus replication, i.e., binding and uptake. The particles themselves are more thermolabile than those of wild-type SFV, suggesting that the 6K protein may be a part of the structure of wild-type virus or that the slower budding leads to an altered configuration of the trimeric spikes. These data support other studies that implicate the 6K protein as an important but nonessential component in the assembly and budding of the alphavirus particle, perhaps by affecting the packing of the glycoproteins and their interactions with membrane lipid.
甲病毒基因组编码一种6 kDa的小疏水蛋白（6K蛋白），它作为一种大的多蛋白的一部分被表达，该多蛋白包含两种病毒跨膜糖蛋白的序列，这两种糖蛋白形成感染性颗粒的刺突。尽管6K蛋白的产生量与糖蛋白相当，但在分泌的感染性病毒粒子中发现的6K蛋白却很少。通过使用多种经突变改变的6K形式，研究了该蛋白在病毒复制和结构中的作用，这些形式产生了表型不同的病毒。已从Semliki森林病毒（SFV）的感染性cDNA构建了编码6K蛋白（δ6K）的基因的完全缺失突变体，并转录了RNA产生的子代病毒，该子代病毒与正常病毒非常相似（P. Liljeström、S. Lusa、D. Huylebroeck和H. Garoff，《病毒学杂志》65:4107 - 4113，1991年）。现在对该突变体进行了进一步研究，结果表明δ6K的生长对其宿主细胞有很强的依赖性，其形成速率为野生型SFV的2%至50%。在δ6K突变体的复制中，哺乳动物细胞比昆虫和禽类细胞缺陷得多。该突变体在糖蛋白的形成和运输或核衣壳的产生方面没有缺陷，核衣壳在感染的BHK细胞的质膜上积累。因此，主要缺陷在于新病毒的最终组装和出芽。在感染了δ6K毒株的BHK细胞中，通过对彻底洗涤过的细胞进行渗透裂解，可以回收相当大比例的总感染性病毒。完全缺乏6K的感染性SFV在病毒复制的早期阶段，即结合和摄取阶段，与野生型SFV相同。这些颗粒本身比野生型SFV的颗粒对热更不稳定，这表明6K蛋白可能是野生型病毒结构的一部分，或者较慢的出芽导致三聚体刺突的构型改变。这些数据支持了其他研究，这些研究表明6K蛋白是甲病毒颗粒组装和出芽中的一个重要但非必需的成分，可能是通过影响糖蛋白的包装及其与膜脂的相互作用来实现的。
