Figure 1.

Inhibition of polyadenylation by dephosphorylation of components in the HeLa nuclear extract. HeLa nuclear extract was incubated with increasing amounts of calf intestinal alkaline phosphate (0.01 U/μg to 0.08 U/μg) for 30 minutes at 30°C. The samples were then assayed for 3′ end processing using a full-length SV40 mRNA substrate under Mg²⁺ conditions. One sample (lane 1) consisted of untreated HeLa extract in the presence of 3′ dATP and Mg²⁺ to detect the upstream cleavage product. Arrows a, b, and c correspond to the polyadenylated RNA, −58/+55 SV40 late pre-mRNA (containing the upstream and downstream recognition sequences and the cleavage site), and the 5′ cleavage product, respectively. Lanes 2 to 8 correspond to samples incubated with 0, 0.015, 0.02, 0.03, 0.04, 0.06, and 0.08 U/μg of alkaline phosphatase, respectively.