The classical swine fever virus (CSFV) nonstructural protein p7 is crucial for virus production, yet precisely how the p7 modulates this process is unclear. In this study, we first identified the interactions of p7 with E2 and NS2. The key binding regions of both p7 and NS2 mapped to the first transmembrane (TM1) domain of two proteins. Three amino acid substitutions in the TM1 region of p7 (p7^{TDI18/19/20AAA}, p7^{EVV21/22/23AAA} and p7^{YFY25/26/30AAA}) impaired infectious virus production and reduced the interaction of p7 with the NS2 protein. The E2p7 processing and mature p7, but not the E2p7 precursor, are essential for infectious virus production. Bicistronic mutants (pSM/E2/IRES) with single substitutions at residues 1 to 9 of p7 exhibited a significantly increased infectious CSFV titer compared to their counterparts in the context of pSM. Viral genomic RNA copies of the mutants exhibited similar levels compared with the wt CSFV. Our results demonstrated that CSFV p7 and its precursor E2p7 modulate viral protein interactions and infectious virus production without influencing viral RNA replication.

中文翻译：

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古典猪瘟病毒非结构蛋白p7调节传染性病毒的产生。

经典的猪瘟病毒（CSFV）非结构蛋白p7对于病毒产生至关重要，但p7究竟如何调节这一过程尚不清楚。在这项研究中，我们首先确定了p7与E2和NS2的相互作用。p7和NS2的关键结合区都映射到两个蛋白质的第一个跨膜（TM1）域。p7（p7 ^{TDI18 / 19 / 20AAA}，p7 ^{EVV21 / 22 / 23AAA}和p7 ^{YFY25 / 26 / 30AAA）}在TM1区的三个氨基酸取代）损害了感染性病毒的产生，并降低了p7与NS2蛋白的相互作用。E2p7加工和成熟的p7（而不是E2p7前体）对于感染性病毒的生产至关重要。在p7的情况下，在p7的1至9位残基处单取代的双顺反子突变体（pSM / E2 / IRES）表现出明显的感染性CSFV滴度。与wt CSFV相比，突变体的病毒基因组RNA拷贝显示出相似的水平。我们的结果表明，CSFV p7及其前体E2p7可调节病毒蛋白相互作用和感染性病毒的产生，而不会影响病毒RNA的复制。