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The design used for generating chimeric virus. F1, F2, and F3 were RT-PCR amplified from the region covering 5′ UTR until the end of ORF1ab of RespPRRSV. F4 was amplified from Hun4 F112 strain. The purified F1–F4 fragments were assembled into the modified pSMART BAC. After transfecting into a 293T-MARC-145 coculture, a chimeric virus displaying ORF1ab of RespPRRSV and ORFs 2–7 of Hun4 F112 was obtained.
