Polyadenylation

Useful videos polyadenylation of mRNA (poly a tail) and polyadenylation 

CPSF (cleavage and polyadenylation specificity factor) and CstF (cleavage stimulating factor) bind to the polyadenylation signal sequence (AAUAAA) and a GU-rich region of mRNA, respectively. Cleavage factor (an endonuclease) is recruited to cleave mRNA right before the GU-rich region, resulting in the dissociation of CstF. Polyadenylation binding protein is recruited. Pol II starts to synthesize the polyA tail. When ~10 polyA is formed, CPSF disengages. Pol II detaches. PolyA binding protein coats the polyA tail, and mediates the circularisation of polyA tail with the 5'-cap of mRNA.