FIGURE 4.

An intronic cis-acting element associated with 3′end cleavage and polyadenylation down-regulates IL7R exon 6 inclusion. (A) Schematics of the IL7R exon 6/intron 6 region showing the presence of the consensus polyadenylation signal AAUAAA in intron 6, 16 nt downstream from the exon 6 5′ splice site, followed by the cleavage signal (“CA”) 19 nt downstream from the poly(A) sequence. The substitution mutation used to assess effect of the intronic poly(A) signal on exon 6 inclusion is shown (pAmut). (B) Mutation to the intronic AAUAAA sequence results in increased inclusion of exon 6. Two minigenes, “C” and sub(36–40), were analyzed either with (right) or without (left) the poly(A) signal mutation in intron 6. Minigenes were transfected into HeLa cells, and exon 6 inclusion analyzed as in Figure 2.