Protein diversity in complex organisms such as humans is not achieved through a vast number of genes, but instead by creating multiple, alternatively spliced mRNA variants from one gene. Especially in neurons, multiple RNA-protein interactions balance exon in- or exclusion into an mRNA and any imbalance of this process can impair neuronal functions and lead to neurological diseases. Despite its importance, little is known how alternative splicing is regulated at the molecular level. We will use a combination of biochemical methods and NMR spectroscopy to study how multiple RNA-protein interactions regulate splice site accessibility and thereby modulate mRNA composition and subsequent gene expression.