title: Recognition of exonic splicing enhancer sequences by the Drosophila splicing repressor RSF1.
abstract: The Drosophila repressor splicing factor 1 (RSF1) comprises an N-terminal RNA-binding region and a C-terminal domain rich in glycine, arginine and serine residues, termed the GRS domain. Recently, RSF1 has been shown to antagonize splicing factors of the serine/arginine-rich (SR) family and it is, therefore, expected to play a role in processing of a subset of Drosophila pre-mRNAs through specific interactions with RNA. To investigate the RNA-binding specificity of RSF1, we isolated RSF1-binding RNAs using an in vitro selection approach. We have identified two RNA target motifs recognized by RSF1, designated A (CAACGACGA)- and B (AAACGCGCG)-type sequences. We show here that the A-type cognate sequence behaves as an SR protein-dependent exonic splicing enhancer. Namely, three copies of the A-type ligand bind SR proteins, stimulate the efficiency of splicing of reporter pre-mRNAs several fold and lead to inclusion of a short internal exon both in vitro and in vivo. However, three copies of a B-type ligand were much less active. The finding that RSF1 acts as a potent repressor of pre-mRNA splicing in vitro led us to propose that the equilibrium between a limited number of structurally-related general splicing activators or repressors, competing for common or promiscuous binding sites, may be a major determinant of the underlying mechanisms controlling many alternative pre-mRNA process-ing events.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002460:Cell Line; D004330:Drosophila; D029721:Drosophila Proteins; D004742:Enhancer Elements, Genetic; D005091:Exons; D005914:Globins / Q000235:genetics; D006367:HeLa Cells; D006801:Humans; D019476:Insect Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D012326:RNA Splicing; D000072260:RNA Splicing Factors; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D000068103:Serine-Arginine Splicing Factors