A novel mutation in the neurofibromatosis type 1 (NF1) gene promotes skipping of two exons by preventing exon definition11Edited by M. Yaniv

Using a protein truncation assay, we have identified a new mutation in the neurofibromatosis type 1 (NF1) gene that causes a severe defect in NF1pre-mRNA splicing. The mutation, which consists of a G to A transition at position +1 of the 5′ splice site of exon 12a, is associated with the loss of both exons 11 and 12a in the NF1mRNA. Through the use of in vivoand in vitrosplicing assays, we show that the mutation inactivates the 5′ splice site of exon 12a, and prevents the definition of exon 12a, a process that is normally required to stimulate the weak 3′ splice site of exon 12a. Because the 5′ splice site mutation weakens the interaction of splicing factors with the 3′ splice site of exon 12a, we propose that exon 11/exon 12a splicing is also compromised, leading to the exclusion of both exons 11 and 12a. Our results provide in vivosupport for the importance of the exon definition model during NF1splicing, and suggest that the NF1region containing exons 11 and 12a plays an important role in the activity of neurofibromin.