Ekström M, Liljeström P, Garoff H
Department of Molecular Biology, Karolinska Institute, Huddinge, Sweden.
EMBO J. 1994 Mar 1;13(5):1058-64. doi: 10.1002/j.1460-2075.1994.tb06354.x.
Semliki Forest virus, SFV, directs the synthesis of two membrane proteins, p62 and E1, which form a p62E1 heterodimer in the endoplasmic reticulum. After being transported to the plasma membrane (PM), they are incorporated into the virus membrane during the process of virus budding. Electronmicroscopic analyses of the envelope in matured virus show that the heterodimers are clustered into trimeric structures (spikes) which further form a regular surface lattice with T = 4. In this work we have used a genetic approach to study the importance of the trimerization event for virus budding. We have coexpressed a budding competent form of the virus heterodimer with another one which cannot be used for particle formation because of a defect in nucleocapsid (NC) binding. We show that the NC binding-deficient heterodimer is able to inhibit the budding of the competent one in a concentration-dependent manner and that the NC binding-competent heterodimers can rescue the incompetent ones into virus particles. This suggests that the heterodimers are complexed together, probably into the trimeric structures (spikes), at the PM to expose a multivalent binding site for the NC and thereby drive efficient virus budding.
塞姆利基森林病毒（SFV）指导合成两种膜蛋白，即p62和E1，它们在内质网中形成p62E1异二聚体。在被转运到质膜（PM）后，它们在病毒出芽过程中被整合到病毒膜中。对成熟病毒包膜的电子显微镜分析表明，异二聚体聚集成三聚体结构（刺突），这些刺突进一步形成具有T = 4的规则表面晶格。在这项工作中，我们采用了一种遗传学方法来研究三聚化事件对病毒出芽的重要性。我们将一种具有出芽能力的病毒异二聚体与另一种由于核衣壳（NC）结合缺陷而不能用于病毒粒子形成的异二聚体共表达。我们发现，缺乏NC结合能力的异二聚体能够以浓度依赖的方式抑制具有出芽能力的异二聚体的出芽，并且具有NC结合能力的异二聚体能够将缺乏出芽能力的异二聚体拯救到病毒粒子中。这表明异二聚体在质膜处聚集在一起，可能形成三聚体结构（刺突），以暴露一个用于NC的多价结合位点，从而驱动高效的病毒出芽。
