Cleavage stimulatory factor

Cleavage stimulatory factor or cleavage stimulation factor (CstF or CStF) is a heterotrimeric protein of about 200 kilodaltons that is involved in the cleavage of the 3' signaling region from a newly synthesized pre-messenger RNA (mRNA) molecule. CstF is recruited by cleavage and polyadenylation specificity factor (CPSF) and assembles into a protein complex on the 3' end to promote the synthesis of a functional polyadenine tail, which results in a mature mRNA molecule ready to be exported from the cell nucleus to the cytoplasm for translation.

The amount of CstF in a cell is dependent on the phase of the cell cycle, increasing significantly during the transition from G0 phase to S phase.