Interferon induces a unique protein in mouse cells bearing a gene for resistance to influenza virus.

Mouse cells carrying the dominant resistance gene Mx develop a more efficient antiviral state toward influenza viruses in response to interferon than do Mx-negative cells. We have identified an Mx gene-associated product by labeling cultured peritoneal macrophages and embryonic cells with [35S]methionine in the presence or absence of interferon. The radioactive proteins from unfractionated cytoplasmic extracts were separated electrophoretically in two dimensions and were revealed by fluorography. A protein with a Mr of 72,500 and an isoelectric point of 6.3 was induced by mouse interferon type I (a mixture of alpha and beta interferons) in cells carrying the gene Mx but not in cells lacking Mx. The induction of this protein could be blocked by actinomycin D. The maximal rate of synthesis was reached in embryonic cells 4-5 hr after treatment with 10(3) reference units of interferon per ml. When the allele Mx (present in the inbred mouse strain A2G) was repeatedly backcrossed on different genetic backgrounds (BALB/c, C57BL/6, A/J), a clear correlation between the inducibility by interferon of this protein and the presence of the allele Mx was observed. The results suggest that this protein induced by the interaction of interferon with Mx plays a role in the selective antiviral state against influenza viruses that is observed in interferon-treated Mx-bearing cells.