A novel gene constitutively expressed in human lymphoid cells is inducible with interferon-γ in myeloid cells

A cluster of at lest six interferon-γ (IFNγ)-inducible genes designated Ifi201-204 and located on mouse chromosome 1 has recently been described. Here, we report a human IFN-γ-inducible gene, IFI 16, which has nucleotide sequence similarity with portions of two of the mouse genes, Ifi202 and Ifi204. A full-length cDNA clone derived from IFI 16 [2.709 kilobases (kb)] contained a single open reading frame of 2.187 kb which encoded a putative polypeptide of 729 amino acids and a predicted non-glycosylated M_r of 80020. IFI 16 mRNA was found to be constitutively expressed in lymphoid cells and in cell lines of both the T and B lineages. By contrast, the mRNA was not expresed by the cell lines HL-60, U937, and K562, which represent early stages of myeloid development, but was strongly inducible in HL-60 and U937 with IFN-γ. The IFI 16 protein demonstrated a putative domain structure with patchy similarity to the proteins expressed from gene Ifi202 and Ifi204. The mouse and human proteins each contain two analogous ≈200 amino acid domains which are imperfect copies, but IFI 16 demonstrated additional unique regions, including a Lys-rich N-terminal portion and a "spacer" region between the reiterated domains, analogous to spacer regions in the CD5 and CD8α molecules. Using a panel of inter-species somatic cell hybrid cell lines, IFI 16 was localized to the chromosomal region 1q12→1qter, a region systenic between mouse an man. DNA blotting indicated that, in contrast to the mouse, IFI 16 is present as a single copy gene in the human genome. The authors are pleased to make the cDNA clones described in this paper available to interested investigators.