Poly(A) polymerase has no specificity for any particular RNA sequence, as well as a very low affinity for the RNA. Under physiological conditions, the activity of poly(A) polymerase depends on two auxiliary factors, both of which bind to specific RNA sequences and recruit the poly(A) polymerase by a direct contact. One of these proteins is the heterotetrameric CPSF, which binds the AAUAAA sequence and is also essential for 3' cleavage.
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