FIG. 5.

Deleting the RNA polymerase pause site further reduces recognition of the modified μs poly(A) signals. The ΔU mutation introduces a NotI restriction site in place of the distal GU-rich element; when the NotI-HindIII fragment containing an RNA Pol II pause site is deleted (ΔNH), the pA/splice ratio decreases (29). The pause site deletion was combined with several of the downstream element mutations that had the NotI restriction site, as shown. “X” indicates that the GU-rich element is mutated; the added GU sequence is indicated in those constructs where present. These constructs were transfected into HepG2 cells, and RNA levels were quantitated by S1 nuclease analysis.