Cleavage stimulation factor

Cleavage stimulatory factor or cleavage stimulation factor (CstF or CStF) is a heterotrimeric protein involved in the cleavage of the 3' signaling region from a newly synthesized pre-messenger RNA (mRNA) molecule. It recognizes U/GU‑rich elements (GREs) downstream of pre‑mRNA cleavage sites and promotes endonucleolytic cleavage and subsequent polyadenylation (poly(A)) of eukaryotic pre‑mRNAs.

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 (poly(A) tail), which results in a mature mRNA molecule ready to be exported from the cell nucleus to the cytosol for translation.

CstF is made up of the proteins CSTF1, CSTF2 and CSTF3, totaling about 200 kDa. CSTF2 is the primary RNA-binding subunit that recognizes GREs downstream of the cleavage site.

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 in mouse fibroblast and human splenic B cells.

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