Bergeron J, Mabrouk T, Garzon S, Lemay G
Département de Microbiologie et Immunologie, Université de Montréal, Québec, Canada.
Virology. 1998 Jul 5;246(2):199-210. doi: 10.1006/viro.1998.9188.
The mutation harbored by the reovirus ts453 thermosensitive mutant has been assigned to the S4 gene encoding the major outer capsid protein sigma 3. Previous gene sequencing has identified a nonconservative amino acid substitution located near the zinc finger of sigma 3 protein in the mutant. Coexpression in COS cells of the sigma 3 protein presenting this amino acid substitution (N16K), together with the other major capsid protein mu 1, has also revealed an altered interaction between the two proteins; this altered interaction prevents the sigma 3-dependent cleavage of mu 1 to mu 1C. This could explain the lack of outer capsid assembly observed during ts453 virus infection at nonpermissive temperature. In the present study, we pursued the characterization of this mutant sigma 3 protein. Although the N16K mutation is located close to the zinc finger region, it did not affect the ability of the protein to bind zinc. In contrast, this mutation, as well as mutations within the zinc finger motif itself, can increase the binding of the protein to double-stranded RNA (dsRNA). It also appears that the N16K mutant protein is more efficiently transported to the nucleus than the wild-type protein, an observation consistent with the postulated role of dsRNA binding in sigma 3 nuclear presence. The lack of association with mu 1, and/or the increased dsRNA-binding activity of sigma 3, could be responsible for a partial resistance of the ts453 virus to interferon treatment and this could have important consequences in the context of protein synthesis regulation during natural reovirus infection.
呼肠孤病毒ts453温度敏感突变体所携带的突变已被定位到编码主要外衣壳蛋白σ3的S4基因上。先前的基因测序已确定该突变体中σ3蛋白锌指附近存在一个非保守氨基酸替换。在COS细胞中共表达呈现此氨基酸替换（N16K）的σ3蛋白与另一种主要衣壳蛋白μ1，也揭示了这两种蛋白之间相互作用的改变；这种相互作用的改变阻止了σ3依赖的μ1向μ1C的裂解。这可以解释在非允许温度下ts453病毒感染期间观察到的外衣壳组装缺失现象。在本研究中，我们对这种突变的σ3蛋白进行了特性研究。尽管N16K突变位于锌指区域附近，但它并不影响该蛋白结合锌的能力。相反，这种突变以及锌指基序本身内的突变，可以增加该蛋白与双链RNA（dsRNA）的结合。似乎N16K突变蛋白比野生型蛋白更有效地转运到细胞核，这一观察结果与dsRNA结合在σ3核定位中的假定作用一致。与μ1缺乏关联和/或σ3的dsRNA结合活性增加，可能是ts453病毒对干扰素治疗产生部分抗性的原因，这在自然呼肠孤病毒感染期间的蛋白质合成调节方面可能具有重要意义。
