Fig. 1.

Coimmunoprecipitation of nonphosphorylated differentially tagged STAT1 proteins. (A) Sites of domain boundaries, point mutations, and epitope tagging are indicated. (B) Diagram of known STAT1 structures (2, 3). The DNA (blue coil)-bound tyrosine-phosphorylated structure is labeled parallel; in this structure, the NDs cannot interact (2). The two antiparallel diagrams are from ref. 3 and are discussed in the Introduction. (C) 293T cells were transfected to express the indicated epitope-tagged proteins: F172W, single mutant; F77A/L78A, double mutant; F172W/F77A/L78A, triple mutant. Cell extracts were immunoprecipitated with anti-Flag antibody (IP:Flag) or anti-Myc antibody (IP:Myc). After precipitation and epitope release, SDS/PAGE and immunoblotting (IB) with anti-Myc or anti-Flag antibody was carried out.