Inhibition is dependent on the nuclear history of the mRNA. A) Plasmid or B) in vitro made mRNA for the indicated constructs was transfected into HEK 293T cells. After 24 hr, Gag expression was quantified by pulse labeling for 1 hr and immunoprecipitating with an MMTV anti-CA antibody. β-catenin immunoprecipitation served as a loading control. Gag expression from plasmid C) or in vitro made mRNA D) was quantified relative to β-catenin. Data represent the average of three experiments ± SD. Pr77gag, the Gag precursor (77 KDa) and β-catenin (98 KDa).