Pre-mRNAs from the D. melanogaster gene dsx contain 6 exons. In males, exons 1,2,3,5,and 6 are joined to form the mRNA, which encodes a transcriptional regulatory protein required for male development. In females, exons 1,2,3, and 4 are joined, and a polyadenylation signal in exon 4 causes cleavage of the mRNA at that point. The resulting mRNA is a transcriptional regulatory protein required for female development^[1].

This is an example of exon skipping alternative splicing. The intron upstream from exon 4 has a weak-consensus polypyrimidine tract, to which U2AF proteins bind poorly without assistance from splicing activators. This 3' splice acceptor site is therefore not used in males. Females, however, produce the splicing activator Transformer (Tra). The SR protein Tra2 is produced in both sexes and binds to an ESE in exon 4; if Tra is present, it binds to Tra2 and, along with another SR protein, forms a complex that assists U2AF proteins in binding to the weak polypyrimidine tract. U2 is recruited to the associated branch point, and this leads to inclusion of exon 4 in the mRNA^[1][2].

Notes

1. ↑ ^{a b} Lynch KW, Maniatis T (August 1996). "Assembly of specific SR protein complexes on distinct regulatory elements of the Drosophila doublesex splicing enhancer". Genes Dev. 10 (16): 2089–101. PMID 8769651.
2. ↑ Graveley BR, Hertel KJ, Maniatis T (June 2001). "The role of U2AF35 and U2AF65 in enhancer-dependent splicing". RNA 7 (6): 806–18. PMID 11421359. PMC: 1370132.