Cleavage and polyadenylation specificity factor (CPSF) (or Cleavage polyadenylation stimulating factor) is involved in the cleavage of the 3' signaling region from a newly synthesized pre-messenger RNA (pre-mRNA) molecule in the process of gene transcription. It is the first protein to bind to the signaling region near the cleavage site of the pre-mRNA, to which the polyadenine tail will be added by polyadenine polymerase.