Figure 1. Analysis of splicing products by denaturing PAGE and autoradiography. ‐labeled β‐globin pre‐mRNA was spliced in vitro with three different batches (A, B, C) of HeLa cell nuclear extracts. The standard splicing reactions (25 µl each) with the indicated volumes of the nuclear extracts were incubated at 30 °C for 4 h. The splicing products were separated with denaturing 5.5% PAGE, and the dried gel was visualized by autoradiography. The structures of the pre‐mRNA and splicing products are shown schematically at the top and side of the panel (sizes are indicated in nucleotides). The ‐labeled DNA Ladder (New England Biolabs, Ipswich, USA) is shown with the sizes indicated (lane M). The asterisk (*) indicates a cleavage product unrelated to splicing. The construction of a plasmid containing a human β‐globin minigene and identification of these splicing products were previously described [ 1, 11].