Structure—Function Analysis of Murine Interferon-γ: Antiviral Properties of Novel Hybrid Interferons

As described earlier the protein products of the murine interferon (IFN) genes MuIFN-α₁, -α₂, and -α₄ differ in their antiviral activity on hamster (CHO) and mouse (L929) cells. For structure—function analysis, hybrids were prepared between the three genes using common restriction enzyme sites. Natural and hybrid genes were transiently expressed in monkey COS cells. Under the conditions used IFN constituted 20-30% of the total amount of secreted proteins. Using a panel of hybrids either between α₁ and β₂ or between α₁, α₂, and α₄, the amino-terminal region of the protein, from amino acids 10 to 58, was found to determine its antiviral activity on hamster cells. On mouse cells, the antiviral activities of hybrids between α₄ and either α₁ or α₂ were compared. The high activity of α₄ (five to ten times that of α₁ or α₂) was not transmitted to hybrids having the amino-terminal part of α₄, but coincided with the presence of the α₄ carboxy-terminal region in all but one hybrid construct. The deletion of five amino acids (positions 103-107) located in this region of α₄ did not affect antiviral activity when introduced into MuIFN-α₂ and a MuIFN-α₄₂ hybrid by site-directed mutagenesis.