Specificity of Stat3β antibody. Whole-cell protein extracts (1 mg) of unstimulated cells were incubated with rabbit polyclonal Stat3-specific antibody (C-20; 1 μg) followed by protein G-Sepharose (left lane) or with chicken Stat3β-specific IgY conjugated to CNBr-activated Sepharose Beads (right lane). Bound proteins were eluted by boiling in SDS-PAGE sample buffer and separated by SDS-PAGE and immunoblotted using Stat3 monoclonal antibody. The positions of the prestained molecular-weight markers are indicated on the left and the positions of the Stat3 and Stat3β bands are indicated on the right. The results shown are representative of two experiments.