The murine Ly-6A/E gene is transcriptionally induced in cells exposed to interferon alpha/beta or gamma (IFN-alpha/beta or IFN-gamma). Analysis of the 5' flanking sequence using reporter plasmids that contain upstream elements of the Ly-6E gene has previously identified an approximately 850-base-pair IFN-responsive region that lacked an IFN-alpha-stimulated response element (ISRE), the element present and required for an IFN-alpha response of a number of genes. Analysis by deletion and stable transfection of the IFN-responsive region of the Ly-6E promoter has defined an 80-base-pair region containing an IFN-gamma activation site (GAS) but no ISRE that allows IFN-gamma and IFN-alpha inducibility of the Ly-6E gene. As tested by specific antiserum, a 91-kDa protein known to be activated in IFN-alpha- or IFN-gamma-treated cells binds to the GAS element from the Ly-6E promoter. The 91-kDa protein exists as an inactive cytoplasmic precursor and depends on tyrosine phosphorylation for its activation. Thus the same 91-kDa protein appears to act in the signal transduction pathways of both types of IFN for the Ly-6-A/E gene.