Department of Diagnostic and Biological Sciences and Institute for Molecular Virology, University of Minnesota, Minneapolis, MN 55455, USA.
J Mol Biol. 2011 Jul 1;410(1):50-9. doi: 10.1016/j.jmb.2011.04.070. Epub 2011 May 5.
Double-stranded DNA bacteriophages and their eukaryotic virus counterparts have 12-fold head-tail connector assemblages embedded at a unique capsid vertex. This vertex is the site of assembly of the DNA packaging motor, and the connector has a central channel through which viral DNA passes during genome packaging and subsequent host infection. Crystal structures of connectors from different phages reveal either disordered residues or structured loops that project into the connector channel. Given the proximity to the translocating DNA substrate, these loops have been proposed to play a role in DNA packaging. Previous models have proposed structural motions in either the packaging ATPase or the connector channel loops as the driving force that translocates the DNA into the prohead. Here, we mutate the channel loops of the Bacillus subtilis bacteriophage φ29 connector and show that these loops have no active role in translocation of DNA. Instead, they appear to have an essential function near the end of packaging, acting to retain the packaged DNA in the head in preparation for motor detachment and subsequent tail assembly and virion completion.
双链 DNA 噬菌体及其真核病毒对应物在独特的衣壳顶点处具有 12 倍的头-尾连接器组装体。该顶点是 DNA 包装马达组装的部位，连接器具有中央通道，病毒 DNA 在基因组包装和随后的宿主感染过程中通过该通道。来自不同噬菌体的连接器的晶体结构揭示了无序残基或突出到连接器通道中的结构环。鉴于与正在转运的 DNA 底物的接近程度，这些环被提议在 DNA 包装中发挥作用。以前的模型提出了包装 ATP 酶或连接器通道环中的结构运动作为将 DNA 转运到前体中的驱动力。在这里，我们突变枯草芽孢杆菌噬菌体 φ29 连接器的通道环，结果表明这些环在 DNA 的转运过程中没有发挥积极作用。相反，它们在包装的后期似乎具有重要功能，作用是在马达分离和随后的尾部组装以及病毒体完成之前，将包装的 DNA 保留在头部中。
