Wang S, Palasingam P, Nøkling R H, Lindqvist B H, Dokland T
Institute of Molecular Agrobiology, The National University off Singapore, 117604 Singapore.
Virology. 2000 Sep 15;275(1):133-44. doi: 10.1006/viro.2000.0521.
Bacteriophage P4 is a satellite virus of bacteriophage P2, which has acquired the ability to utilize the structural gene products of P2 to assemble its own capsid. The normal P2 capsid has a T = 7 icosahedral structure comprised of the gpN-derived capsid protein, whereas the capsid produced under the control of P4 has a smaller, T = 4 structure. The protein responsible for this size determination is the P4-coded gene product Sid, which forms an external scaffold on the P4 procapsid. Using an in vitro assembly system, we show that gpN and Sid can coassemble into procapsid-like particles, indistinguishable from those produced in vivo, in the absence of any other gene products. The fidelity of the assembly reaction is enhanced by the inclusion of PEG and has a pH optimum between 8.0 and 8.5. Analysis of the assembly properties of truncated versions of Sid and gpN suggests that the amino-terminal part of Sid is involved in gpN binding, while the carboxyl-terminal part forms trimeric Sid-Sid interactions, and that the first 31 amino acids of gpN are required for binding to Sid as well as for size determination.
噬菌体P4是噬菌体P2的一种卫星病毒，它获得了利用P2的结构基因产物来组装自身衣壳的能力。正常的P2衣壳具有由gpN衍生的衣壳蛋白组成的T = 7二十面体结构，而在P4控制下产生的衣壳具有较小的T = 4结构。负责这种大小确定的蛋白质是P4编码的基因产物Sid，它在P4原衣壳上形成外部支架。使用体外组装系统，我们表明在没有任何其他基因产物的情况下，gpN和Sid可以共同组装成原衣壳样颗粒，与体内产生的颗粒无法区分。通过加入聚乙二醇（PEG）可提高组装反应的保真度，其最适pH值在8.0至8.5之间。对Sid和gpN截短版本的组装特性分析表明，Sid的氨基末端部分参与gpN结合，而羧基末端部分形成三聚体Sid-Sid相互作用，并且gpN的前31个氨基酸对于与Sid结合以及大小确定是必需的。
