Cleavage and polyadenylation specificity factor

Cleavage and polyadenylation specificity factor (CPSF) is involved in the cleavage of the 3' signaling region from a newly synthesized pre-messenger RNA (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. The upstream signaling region has the canonical nucleotide sequence AAUAAA, which is highly conserved across the vast majority of pre-mRNAs. A second downstream signaling region, located on the portion of the pre-mRNA that is cleaved before polyadenylation, consists of a GU-rich region required for efficient processing.

CPSF is itself a protein complex of four distinct proteins. It serves to recruit other proteins or complexes, such as cleavage stimulatory factor and the two poorly-understood cleavage factors, to the cleavage site. The binding of the polyadenine polymerase responsible for actually synthesizing the tail is a necessary prerequisite for cleavage, thus ensuring that cleavage and polyadenylation are tightly coupled processes.