Question

A gene encodes a pre-mRNA with 8 exons and 7 introns. A mutation eliminates the 3’ splice site from intron 5. What exons would be found in the mRNA after splicing was completed?

Answer 1

The alternate splicing will occur between the 5’ splice site and the 3’ splice site. Hence, when the 3’ splice site of intron 5 is mutated, it is not recognized by the spliceosome. This will cause the 3’ splice site for intron 6 to be recognized. As a result, intron 5, exon 6 and intron 6 will be spliced out. This is known as exon exclusion.

Thus, intron 1, intron2, intron3, intron 4, intron 5, exon 6, intron 6, and intron 7 are spliced out.

The spliced mRNA will have exon1, exon 2, exon3, exon 4, exon 5, exon 7 and exon 8.