To construct the pISRE-CBG99 vector, we first generated a 5xrepeat of the ISRE sequence and a TATAA box (5xISRE-TATAA) in the pUCMinusMCS vector from Blue Heron Biotechnology (Bothell, WA) and then cloned this sequence into the Chroma-Luc pCBG99-Basic reporter vector from Promega (Madison, WI) and ligated into Xma1 and Nco1 sites using T4 DNA ligase from Life Technologies (Carlsbad, CA). The DNA sequence of the resultant pISRE-CBG99 vector was confirmed by carrying out BigDye Terminator v3.1 sequencing reactions (Life Technologies) on an ABI capillary sequencer. This vector and the pPUR selection vector from Clontech (Mountain View, CA) were co-transfected at a 9:1 ratio into 2fTGH or HEK293T cells to increase the likelihood that cells tolerating puromycin selection (0.5 mg/ml) contained one or more copies of pISRE-CBG99 in addition to pPUR. The 2fTGH cells [49] were obtained from G. Stark (Cleveland Clinic), and HEK293T cells [50, 51] were obtained from T. Brett (Washington University). Transfection was performed using Fugene6 transfection reagent from Roche Applied Science (Indianapolis, IN) . Limiting dilution was used to obtain individual cell clones that were then screened for luciferasemediated luminescence after treatment with IFN-b (1000 U/ml) on a BioTek Synergy 4 multimode plate reader (BioTek, Winooski, VT). Clonal cells exhibiting stable expression were then used for further assay development.