A 15-kD interferon-induced protein and its 17-kD precursor: expression in Escherichia coli, purification, and characterization.

Using recombinant DNA technology, a 15-kD interferon (IFN)-induced protein and its 17-kD precursor have been expressed in Escherichia coli to obtain sufficient quantities of each protein for the investigation of their biological roles. Both the 15-kD and 17-kD proteins have been purified to homogeneity and crystallized. The recombinant 15-kD protein has an identical reversed-phase HPLC elution profile to that of the native 15-kD protein purified from human cells. Furthermore, the recombinant 15-kD and 17-kD proteins have identical amino- and carboxy-terminal amino acid sequences to those predicted from the DNA sequence. The native and recombinant 15-kD proteins give identical tryptic peptide maps, and the recombinant 17-kD protein gives only one additional tryptic peptide. We conclude that the recombinant 17-kD and 15-kD proteins are identical to the 17-kD precursor and the 15-kD stable product synthesized in human cells in response to IFN stimulation. In addition, we have demonstrated that the recombinant 17-kD precursor protein can be converted to the 15-kD protein by cytoplasmic extracts of human cells.