Stat3 and Stat3β supershift analysis of M1 cells clones transfected with wild-type and mutant human G-CSFR constructs. M1 parental cells (P) or clones (two each) expressing either wild-type (WT) human G-CSFR or constructs containing tyrosine-to-phenylalanine mutations at the indicated tyrosine residues were stimulated with G-CSF (1 ng/mL for 15 minutes) and extracted. EMSA was performed in the presence of antibody specific for either Stat3β (A and B) or Stat3 (C and D). (A and C) Autoradiographs of EMSA gels of M1 parental cells and a representative clone containing each construct. The position of the supershifted and nonsupershifted Stat3 and Stat3β are indicated on the right. The signal remaining within the nonsupershifted Stat3 band (B) and the nonsupershifted Stat3β band (D) obtained from M1 parental cells and both clones containing each construct were quantitated by PhosphoImager analysis and the mean ± SEM shown.