Polyadenylation is the addition of a "tail" of adenylate residues to an RNA transcript about 20 bases downstream of the AAUAAA sequence within the three prime untranslated region. Polyadenylation of mRNA has a strong effect on its nuclear transport, translation efficiency, and stability. All of these as well as the process of polyadenylation depend on binding of specific RBPs. All eukaryotic mRNAs with few exceptions are processed to receive 3' poly (A) tails of about 200 nucleotides. One of the necessary protein complexes in this process is CPSF. CPSF binds to the 3' tail (AAUAAA) sequence and together with another protein called poly(A)-binding protein, recruits and stimulates the activity of poly(A) polymerase. Poly(A) polymerase is inactive on its own and requires the binding of these other proteins to function properly.