Fig. 4. Stat1 domains required to suppress expression of c–myc mRNA. U3A cells reconstituted with a Stat1 tyrosine (U3A Stat1 Y701F) or serine (U3A Stat1 S727A) phosphorylation site mutant or with wild-type Stat1α (Kumar et al., 1997b; see for expression levels) were treated with 1500 IU/ml of human IFN–γ. c–myc and GAPDH RNA levels were determined by Northern blot analysis.