Question

You are studying a gene that has four exons. You find that in some cell types the mature mRNA contains all four exons while in others exon 3 is missing from the transcript. You suspect that cells that lack exon 3 express a splicing repressor. Which splice site do you think this repressor acts on to inhibit inclusion of exon 3 (include a drawing)? Explain your reasoning.

Answer 1

The picture of nascent mRNA with four introns and four exons are given below.

Each intron has two splicing sites. For example int 1 has two (named as a and b). similarly Int 2 have c and d, Int 3 has e and f and Int 4 has g and h splicing sites. As the exn 3 is also spliced out with Int 3 and Int 4, f and g splicing sites should contain mutations, so Int 3 and Int 4 are eliminated together with exon 3 lying in between.