School of Molecular and Cellular Biology, Faculty of Biological Sciences and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, UK.
Department of Medical Microbiology and Parasitology, Faculty of Basic Medical Sciences, College of Health Sciences, University of Ilorin, Ilorin, Nigeria.
FASEB J. 2021 Feb;35(2):e21215. doi: 10.1096/fj.202001473RR. Epub 2020 Nov 23.
For gene duplication to be maintained, particularly in the small genomes of RNA viruses, this should offer some advantages. We have investigated the functions of a small protein termed VPg or 3B, which acts as a primer in the replication of foot-and-mouth disease virus (FMDV). Many related picornaviruses encode a single copy but uniquely the FMDV genome includes three (nonidentical) copies of the 3B coding region. Using sub-genomic replicons incorporating nonfunctional 3Bs and 3B fusion products in competition and complementation assays, we investigated the contributions of individual 3Bs to replication and the structural requirements for functionality. We showed that a free N-terminus is required for 3B to function as a primer and although a single 3B can support genome replication, additional copies provide a competitive advantage. However, a fourth copy confers no further advantage. Furthermore, we find that a minimum of two 3Bs is necessary for trans replication of FMDV replicons, which is unlike other picornaviruses where a single 3B can be used for both cis and trans replication. Our data are consistent with a model in which 3B copy number expansion within the FMDV genome has allowed evolution of separate cis and trans acting functions, providing selective pressure to maintain multiple copies of 3B.
为了维持基因复制，特别是在 RNA 病毒的小基因组中，这应该提供一些优势。我们研究了一种称为 VPg 或 3B 的小蛋白的功能，它在口蹄疫病毒 (FMDV) 的复制中充当引物。许多相关的小 RNA 病毒只编码一个拷贝，但独特的是，FMDV 基因组包含三个（非同源）3B 编码区的拷贝。我们使用亚基因组复制子，在竞争和互补测定中包含非功能 3B 和 3B 融合产物，研究了单个 3B 对复制的贡献以及功能的结构要求。我们表明，3B 作为引物发挥作用需要自由的 N 末端，尽管单个 3B 可以支持基因组复制，但额外的拷贝提供了竞争优势。然而，第四个拷贝没有带来进一步的优势。此外，我们发现 FMDV 复制子的跨复制至少需要两个 3B，这与其他小 RNA 病毒不同，其他小 RNA 病毒可以使用单个 3B 进行顺式和反式复制。我们的数据与 3B 拷贝数在 FMDV 基因组中的扩张允许顺式和反式作用功能的独立进化的模型一致，为维持多个 3B 拷贝提供了选择压力。
