FIG. 6.

Phosphorylation and DNA binding of the helix α1 deletion mutant in vitro. Baculovirus-expressed full-length Stat3 (b-ST3-FL) and Stat3 with deletions of the N-domain and helix α1 (b-ST3-ΔN1H) were purified from Sf9 cells and incubated with Src kinase. The reaction mixture was divided so that each part contained 0.5 μg of Stat3 proteins and subjected to either Western blot analysis with the antibodies indicated (A) or EMSA using [³²P]hSIE as a probe (B). FP, free probe.