Fig. 4.

IKKε phosphorylation disrupts the STAT1 homodimer, but not the STAT1:STAT2 heterodimer interface. (A) Space-filling diagram of the S708 (yellow) region and (B) hydrogen-bonding interactions of S708 in the STAT1:STAT1 homodimerization interface (light and dark blue). The diagram is adapted from the 3D structure published by Chen et al. (36) using PyMol. (C) 293T cells were transfected with HA STAT1 and FLAG STAT1 antiparallel (AP) mutants and GFP (mock transfected), IKKε WT, or IKKε K38A. Cells were unstimulated or stimulated with IFNγ. (D) 293T cells were transfected with HA STAT1 and FLAG STAT2 and GFP, IKKε WT, or IKKε K38A. Cells were unstimulated or stimulated with IFNβ. Coimmunoprecipitation experiments were performed using anti-HA matrix beads for the immunoprecipitation (IP) and immunoblotted (IB) for anti-FLAG tagged protein. Input samples were loaded as a control. Experiments were independently repeated at least three times.