WB analysis of samples using GTX24787 Rb (phospho Thr821) antibody prior incubated with the non-phosphopeptide corresponding to the phosphopeptide immunogen (Lane 2), a generic phosphothreonine containing peptide(Lane 3), the phosphopeptide corresponding to Rb (phospho Thr826), or the phosphopeptide immunogen (Lane 5). The data show that only the immunogen phosphopeptide blocks the signal, demonstrating the specificity of the antibody.