SR PROTEINS ARE SUFFICIENT FOR EXON BRIDGING ACROSS AN INTRON

We have developed a defined system to characterize the role of SR prot eins and exonic enhancers in directly promoting splice-site interactio ns across an intron, Using RNA affinity chromatography, we find that S R proteins alone are sufficient to promote the specific association of the enhancer-containing exon 5 with the adjoining exon 6 from avian c ardiac troponin-T. Direct visualization of this exon/exon association by electron spectroscopic imaging shows it to be highly specific, Furt hermore, using in vivo characterized mutants of exon 5, we also show t hat this exon/exon association depends on the splicing enhancer within exon 5. These results suggest a model by which SR proteins may functi on through exonic enhancers to directly promote exon bridging.