Recombinant Chicken Interferon from Escherichia coli and Transfected COS Cells is Biologically Active

We have expressed a cDNA for virus‐induced chick interferon in Escherichia coli. The product, a 19‐kDa protein lacking the signal peptide, was purified to homogeneity from the bacterial inclusion bodies. Proteins in the insoluble fraction of bacterial lysates were dissolved in guanidine hydrochloride and subjected to chromatography on Q‐Sepharose and MonoS columns. Purified recombinant chick interferon has a specific antiviral activity of approximately 108 IU/mg and is a powerful inducer of the interferon‐responsive promoter of the chicken mx gene. Culture medium of transfected COS cells expressing full‐length chick interferon cDNA contained up to 5 × 104 IU antiviral activity/ml that could be neutralized by antibodies to purified recombinant chick interferon. The antibodies precipitated proteins of 23–28 kDa from the supernatants of transfected COS cells. Treatment with endoglycosidase F reduced the size of the immunoprecipitated proteins to approximately 20 kDa, demonstrating that chick interferon is a glycoprotein.