NOVEL EXONIC ELEMENTS THAT MODULATE SPLICING OF THE HUMAN FIBRONECTINEDA EXON

Three exons in the fibronectin primary transcript are alternatively sp liced in a tissue-and developmental stage-specific manner. One of thes e exons, EDA, has been shown previously by others to contain two splic ing regulatory elements between 155 and 180 nucleotides downstream of the 3'-splice site: an exon splicing enhancer and a negative element. By transient expression of a chimeric beta-globin/fibronectin EDA intr on in COS-7 cells, we have identified two additional exonic splicing r egulatory elements. RNA generated by a construct containing the first 120 nucleotides of the fibronectin EDA exon was spliced with an effici ency of approximately 50%. Deletion of most of the fibronectin EDA exo n sequences resulted in a 20-fold increase in the amount of spliced RN A, indicative of an exon splicing silencer. Deletion and mutagenesis s tudies suggest that the fibronectin exon splicing silencer is associat ed with a conserved RNA secondary structure, In addition, sequences be tween nucleotides 93 and 118 of the EDA exon contain a non-purine-rich splicing enhancer as demonstrated by its ability to function in a het erologous context.