Use of a selectable marker regulated by alpha interferon to obtain mutations in the signaling pathway.

Hypoxanthine-guanine phosphoribosyltransferase-negative human cells transfected with a fusion of the upstream region of the IFN-regulated human gene 6-16 and the Escherichia coli gpt gene

Mutagenesis and selection using medium containing hypoxanthine, aminopterin, and thymidine plus IFN or 6-thioguanine plus IFN

Isolation of mutations in the signaling pathway for alpha interferonsurrogate