As the title says, why we have the motif(s) we have in polyadenylation? The first idea is biochemistry, something we see here
source: https://aghunt.wordpress.com/2009/05/14/where-polyadenylation-sirnas-and-dna-methylation-meet/
https://aghunt.wordpress.com/2008/07/18/the-polyadenylation-complex-rna-binding-proteins/
khaognosis 