Western blot using Protein A purified anti-Stat1 pY701 antibody shows detection of phosphorylated Stat1 (indicated by arrowhead at ~91 kDa) in K562 cells after 30 min treatment with 1Ku of hIFN-?? (lane 2). No reactivity is seen for non-phosphorylated Stat1 in untreated cells (lane 1). The membrane was probed with the primary antibody at a 1:1,000 dilution at 4°C, overnight. Personal Communication from Ana Gamero, CCR-NCI, Bethesda, MD.