 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.