Figure 3.

The core binding motif CAUC stimulates in vitro splicing of dsx pre-mRNA. (A) Schematic representation of Drosophila dsx constructs. The dsx exons 3 and 4 are represented by boxes, intron 3 by a solid line. The original enhancer sequences in the dsx female-specific exon 4 were substituted by different sequences indicated below the exon-intron diagram. (B, C) In vitro splicing assay of dsx pre-mRNAs. ³²P-labeled pre-mRNAs were spliced in vitro in HeLa cell nuclear extract for the time indicated. The positions of pre-mRNA, first exon and spliced products are indicated on the right. M, ³²P-labeled pcDNA3 HpaII restriction fragments. (D) In vitro splicing assay of dsx pre-mRNAs in the presence of specific unlabeled RNAs as competitors. ³²P-labeled pre-mRNAs carrying six copies of CAUCUG or CACCUU were spliced in vitro in the absence of any competitors (lanes 2 and 11) or in the presence of ACE sel or ACE sel mut competitors (lanes 3–8 and 12–17). For CAUCUG pre-mRNAs, 600, 1200 and 2400 ng competitor RNAs were used (lanes 3–8). For CACCUU pre-mRNAs, 150, 300 and 600 ng competitor RNAs were added (lanes 12–17).