It's all about splicing of introns ... an OH group at the 3′ end of the exon attacks the phosphodiester bond at the 3′ splice site. The adjoining exons are covalently bound, and the resulting ...

“Often, they will be clustered and usually be within the first 100 or 200 nucleotides within the introns. They can also be within the exon.” RBP splicing factors are sequence-specific, binding to ...