The bovine interferon-γ gene cloned from total RNA of peripheral blood lymphocytes stimulated with concanavalin A (ConA), using the reverse transcriptase-polymerase chain reaction (RT-PCR), was cloned into pGEM T-easy vector and sequenced. The mature peptide without signal peptide was then subcloned and constructed into the expression plasmids pET28a/BoIFN-γ and pPICZα/BoIFN-γ, respectively. The former was highly expressed, induced by isopropyl β-d-thiogalactoside (IPTG), in Escherichia coli BL21, with 30% of bacterial proteins in inclusion bodies. The latter was expressed in Pichia pastoris GS115 with methanol induction. The expressed products were secreted directly into cultural supernatant at concentrations of 1.0 g/l. The same recombinant proteins had antiviral activities 10 times higher in an MDBK (Madan-Darby bovine kidney)/VSV (Vesicular stomatitis virus) cell line than in a CEF (chicken embryo fibroblast)/VSV) cell line, and the antiviral activities expressed in P. pastoris were higher than those expressed in E. coli in the same cell line.
