Figure 5.
Effect of mutations on STAT3 homodimer binding to DNA. (A) WT or mutant pY-STAT3 homodimers that were expressed and purified from bacteria were analyzed for binding to immobilized duplex hSIE DNA by SPR. Equilibrium RU values shown were calculated from sensograms shown in supplemental Figure 7 and plotted against STAT3 protein concentration. (B) KD values were determined by fitting the data to a 1-site equilibrium–binding model. The results shown are the mean of 6 experiments. Each KD value was divided by the WT result for that experiment to determine the relative KD value and the mean relative KD of the 6 experiments shown; the dash (−) indicates the relative KD could not be calculated. (C) Protein lysates of STAT3−/− MEF cells that expressed Ac-GFP1–tagged WT or mutant STAT3α and incubated without or with IL6/sIL6R were examined using the TransAM STAT3 DNA-binding assays. The mean ± SEM of 3 assays is shown (∗P < .0001; Student t test).