A, Human β-globin pre-mRNA was incubated with HeLa nuclear extracts. For reconstitution assay, 20 ng of recombinant TFIP11 was added in the splicing reaction. B, TFIP11 expression in nuclear extracts of HeLa cells transfected with negative silencer or TFIP11 siRNA was detected by immunoblot using rabbit-generated antibody against TFIP11 and β–actin included as control. C, Quantitation of the lariat intron fraction. Error bar represents the standard error of mean. Statistically significant comparison data indicated by *, p < 0.05.