Biology Department, University of York, York, United Kingdom.
Biology Department, University of York, York, United Kingdom
J Virol. 2019 Nov 13;93(23). doi: 10.1128/JVI.01328-19. Print 2019 Dec 1.
Genetic exchange mediated by viruses of bacteria (bacteriophages) is the primary driver of rapid bacterial evolution. The priority of viruses is usually to propagate themselves. Most bacteriophages use the small terminase protein to identify their own genome and direct its inclusion into phage capsids. Gene transfer agents (GTAs) are descended from bacteriophages, but they instead package fragments of the entire bacterial genome without preference for their own genes. GTAs do not selectively target specific DNA, and no GTA small terminases are known. Here, we identified the small terminase from the model GTA, which then allowed prediction of analogues in other species. We examined the role of the small terminase in GTA production and propose a structural basis for random DNA packaging. Random transfer of any and all genes between bacteria could be influential in the spread of virulence or antimicrobial resistance genes. Discovery of the true prevalence of GTAs in sequenced genomes is hampered by their apparent similarity to bacteriophages. Our data allowed the prediction of small terminases in diverse GTA producer species, and defining the characteristics of a "GTA-type" terminase could be an important step toward novel GTA identification. Importantly, the GTA small terminase shares many features with its phage counterpart. We propose that the GTA terminase complex could become a streamlined model system to answer fundamental questions about double-stranded DNA (dsDNA) packaging by viruses that have not been forthcoming to date.
细菌病毒（噬菌体）介导的遗传交换是细菌快速进化的主要驱动力。病毒的首要任务通常是自我繁殖。大多数噬菌体使用小终止酶蛋白来识别自己的基因组，并指导其包含在噬菌体衣壳中。基因转移剂（GTAs）是噬菌体的后代，但它们不偏向于自己的基因，而是包装整个细菌基因组的片段。GTAs 不选择性地针对特定的 DNA，也没有已知的 GTA 小终止酶。在这里，我们鉴定了模型 GTA 的小终止酶，然后可以预测其他物种的类似物。我们研究了小终止酶在 GTA 产生中的作用，并提出了随机 DNA 包装的结构基础。细菌之间任何和所有基因的随机转移都可能对毒力或抗微生物耐药性基因的传播产生影响。由于 GTAs 与噬菌体明显相似，因此发现测序基因组中真正存在的 GTAs 受到阻碍。我们的数据允许预测不同 GTA 产生物种中的小终止酶，并定义“GTA 型”终止酶的特征可能是识别新 GTA 的重要步骤。重要的是，GTA 小终止酶与其噬菌体对应物具有许多共同特征。我们提出，GTA 终止酶复合物可以成为一个简化的模型系统，以回答迄今为止尚未得到解答的关于未包装的双链 DNA（dsDNA）的病毒包装的基本问题。
