STAT3 proteins containing S mutations have decreased interaction with TRiC. In vitro transcription/translation reactions were performed in RLL containing ³⁵S-methionine and equivalent amounts of cDNA constructs encoding WT or mutant STAT3 without or with exogenous bovine TRiC (120 nM; TRiC) as indicated. In the top half of panels A and B, an equivalent fraction of each reaction was separated by sodium dodecyl sulfate polyacrylamide gel electrophoresis, in the case of panel A either before (Input) or after immunoprecipitation with anti-TRiC (TRiC-IP; column E) or control antibody (column C). Gels were dried and autoradiographed. In the bottom half of panels A and B, bands from multiple experiments (N as indicated or ≥3 where noted) were quantitated by densitometry and the mean ± SD plotted for each STAT3 cDNA construct. Differences in means of mutant constructs from WT are indicated by asterisks (*,** P < .001, Student t test).