FIGURE 4.

CELF proteins inhibit NM exon splicing in vitro. (A) Schematic representation of EF1a-NM RNA, with the NM branch point and pyrimidine tract indicated by the circle and rectangle. The sequence from the NM 3′ splice site to 296 nt upstream is shown with the branch point (indicated by the Å) 191 nt upstream. CUG and UG repeats are shown in bold, and the single UCUU motif is bold underlined. (B) ³²P-labeled EF1a-NM α-actinin transcript was spliced in HeLa nuclear extracts for 2 h in the presence of 0–6 μM CELF proteins or 0–4 μM of the unrelated RNA-binding protein UNR (Hunt et al. 1999). RNA species were resolved on 6% polyacrylamide gels. The initial transcripts, splicing intermediates, and products are indicated next to the gels. ETR3, CUG-BP, and CELF4 inhibited NM exon splicing.