Fig. 2. CBP80 but not eIF4E is detectably bound to intron-containing pre-mRNA. (A) As in Figure 1, except that only nuclear fractions and Gl pre-mRNA rather than Gl mRNA were analyzed. Furthermore, mouse anti-eIF4E antibody was used instead of rabbit anti-eIF4E antibody and mouse IgG served to control for non-specific immunopurification using mouse anti-eIF4E antibody. (B) As in (A) except that rabbit anti-eIF4E antibody was used in place of mouse anti-eIF4E antibody and the analysis of MUP mRNA was omitted. (C) As in (A) except that SV40 pre-mRNA and mRNA were analyzed. Results are representative of other independently performed experiments, including those using rabbit anti-eIF4E antibody and NRS as a control. Taking the sum of Gl or SV40 pre-mRNA immunopurified by anti-CBP80 antibody and anti-eIF4E antibody in each panel as 100%, the amount of CBP80-bound pre-mRNA was 96 ± 6% and the amount of eIF4E-bound pre-mRNA was 4 ± 6%.