Overlap Primer Walk PCR (OPW-PCR). In 1st round of PCR, Primer F5 and F5/ were used to introduce enterokinase cleavage site at 5’ end of chimeric gene products IFNα2b-NS3-LAP and LAP-NS3-IFNα2b respectively. In 2nd round of PCR, primer F6 introduced Gly-Ser spacer, His-Tag, Kex2 and XhoI restriction site at 5’ end of the PCR product of 1st round.