Construction of SARS-CoV-2 full - length S gene with point mutations relevant for COVID-19 vaccine strain candidate

To overcome the pandemic of COVID-19, prevent the disease or its post-conditions effectively, a vaccine with the updates of viral strains is needed. The full S gene encoding the glycoprotein spike of SARS-CoV-2 was recommended for vaccine production by the World Health Organization. To create a vaccine strain candidate for a COVID-19, we have cloned the full-length S gene of the SARS-CoV 2 containing mutations that improve thermal stability of the protein (HexaPro) and three strain-specific mutations of D614G, L452R and E484Q that are present in rapidly and widely circulating variants. The fragments of the full-length S gene were first amplified from the two commercial plasmids, in which one plasmid contains the HexaPro mutations and the other was used to amplify the 3’ fragment of the gene, these fragments were then assembled. Strain-specific mutations were generated using primers with mutations. The measles (MeV) overlaping sequences and AscI (5’- GCGCGC-3’) restriction sites were also added to the two ends of the S gene. The full length of the cloned S gene with mutations and restriction sites was confirmed by sequencing and is ready to be inserted into the measles backbone for creating a chimeric genome of MeV_SARS CoV-2.