Figure 4.

PIASy does not block the DNA binding activity of Stat1. (A) Electrophoretic mobility-shift assay analysis. Nuclear extracts prepared from Daudi cells untreated or treated with IFN-α were mixed with a ³²P-labeled Stat1 binding oligonucleotide (11) in the absence (lanes 1, 2, 10, and 11) or presence of various amounts of GST (lanes 3–5 and 12–14), GST-PIASy (lanes 6–9), or GST-PIAS1 (lanes 15–17) as indicated. (B) Same as A except purified tyrosine-phosphorylated Stat1 (lanes 1 and 7–13) or purified unphosphorylated Stat1 (lanes 2–6) was mixed with increasing concentrations of GST or GST-PIASy (30, 90, and 300 ng).