Here another clip from the research paper on how they created their own viruses for testing purposes of SARS-CoV.
Construction of recombinant viruses
Recombinant viruses with the S gene of the novel bat SARSr-CoVs and the backbone of the infectious clone of SARSr-CoV WIV1 were constructed using the reverse genetic system described previously [23] (S9 Fig). The fragments E and F were re-amplified with primer pairs (FE, 5’-AGGGCCCACCTGGCACTGGTAAGAGTCATTTTGC-3’, R-EsBsaI, 5’-ACTGGTCTCTTCGTTTAGTTATTAACTAAAATATCACTAGACACC-3’) and (F-FsBsaI, 5’-TGAGGTCTCCGAACTTATGGATTTGTTTATGAG-3’, RF, 5’-AGGTAGGCCTCTAGGGCAGCTAAC-3’), respectively. The products were named as fragment Es and Fs, which leave the spike gene coding region as an independent fragment. BsaI sites (5’-GGTCTCN|NNNN-3’) were introduced into the 3’ terminal of the Es fragment and the 5’ terminal of the Fs fragment, respectively. The spike sequence of Rs4231 was amplified with the primer pair (F-Rs4231-BsmBI, 5’-AGTCGTCTCAACGAACATGTTTATTTTCTTATTCTTTCTCACTCTCAC-3’ and R-Rs4231-BsmBI, 5’-TCACGTCTCAGTTCGTTTATGTGTAATGTAATTTGACACCCTTG-3’). The S gene sequence of Rs7327 was amplified with primer pair (F-Rs7327-BsaI, 5’-AGTGGTCTCAACGAACATGAAATTGTTAGTTTTAGTTTTTGCTAC-3’ and R-Rs7327-BsaI, 5’- TCAGGTCTCAGTTCGTTTATGTGTAATGT AATTTAACACCCTTG-3’). The fragment Es and Fs were both digested with BglI (NEB) and BsaI (NEB). The Rs4231 S gene was digested with BsmBI. The Rs7327 S gene was digested with BsaI. The other fragments and bacterial artificial chromosome (BAC) were prepared as described previously. Then the two prepared spike DNA fragments were separately inserted into BAC with Es, Fs and other fragments. The correct infectious BAC clones were screened. The chimeric viruses were rescued as described previously [23].