Mutations of the cleavage site and the U-rich element in the 3′flanking sequence affect 3′end processing in a cell line expressing the endogenous F2 gene. (A) Comparison of the F2 3′end mRNA structure by ribonuclease protection analysis of transfected HeLa cells (lane 1) and HepG 2 and HUH-7 cells (lanes 3-4). (B) Modified PAT analysis of cytoplasmic RNA of HUH-7 cells transfected with tandem constructs shown in Figures 2 and 6B. The numbers shown below the panel reflect semiquantitative estimates of the signals generated by limited PCR.