Department of Biology and Viral Information Institute, San Diego State University, 5500 Campanile Drive, San Diego, CA, 92182, USA.
Department of Biology and Viral Information Institute, San Diego State University, 5500 Campanile Drive, San Diego, CA, 92182, USA.
Virology. 2020 Apr;543:7-12. doi: 10.1016/j.virol.2020.01.008. Epub 2020 Jan 18.
An essential step in the morphogenesis of tailed bacteriophages is the joining of heads and tails to form infectious virions. Our understanding of the maturation of complete virus particles remains incomplete. Through an unknown mechanism, phage T4 gene product 4 (gp4) plays an essential role in the head-tail joining step of T4-like phages. Alignment of T4 gp4 homologs identified a type II restriction endonuclease motif. Purified gp4 from both T4 and a marine T4-like bacteriophage, YC, have non-specific nuclease activity in vitro. Mutation of a single conserved amino acid residue in the endonuclease fold of T4 and YC gp4 abrogates nuclease activity. When expressed in trans, the wild type T4 gp4, but neither the mutated T4 protein nor the YC homolog, rescues a T4 gene 4 amber mutant phage. Thus the nuclease activity appears essential for morphogenesis, potentially by cleaving packaged DNA to enable the joining of heads to tails.
长尾噬菌体形态发生的一个重要步骤是将头部和尾部连接起来形成感染性病毒粒子。我们对完整病毒颗粒成熟过程的了解仍然不完整。噬菌体 T4 基因产物 4（gp4）通过未知机制在 T4 样噬菌体的头部-尾部连接步骤中发挥重要作用。T4 gp4 同源物的比对确定了一种 II 型限制内切酶基序。从 T4 和一种海洋 T4 样噬菌体 YC 中纯化的 gp4 在体外具有非特异性核酸酶活性。T4 和 YC gp4 的内切酶折叠中单个保守氨基酸残基的突变会破坏核酸酶活性。当在转译中表达时，野生型 T4 gp4 但不是突变的 T4 蛋白或 YC 同源物，拯救了 T4 基因 4 琥珀突变噬菌体。因此，核酸酶活性似乎对形态发生至关重要，可能通过切割包装的 DNA 来促进头部与尾部的连接。
