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Cell Signaling & Neuroscience

RNA Polyadenylation

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Figure-3b

RNA Polyadenylation

Cleavage-and-polyadenylation specificity factor (CPSF) binds to an upstream AAUAAA polyadenylation signal. Cleavage stimulation factor (CStF) binds to a downstream GU- or U-rich sequence and also interacts with bound CPSF forming a loop in the RNA. Subsequent binding of cleavage factor I (CFI) and CFII help to stabilize the complex. Binding of poly(A) polymerase (PAP) then stimulates cleavage at a site usually 10 to 35 nucleotides 3’ of the upstream polyadenylation signal. The cleavage factors are then released, as is the downstream RNA cleavage product, which is then rapidly degraded. Bound PAP then adds 12 A residues at a slow rate to the 3’-hydroxyl group generated by the cleavage reaction. Finally, binding of poly(A)-binding protein II (PABII) binds to the initial short poly(A) tail and accelerates its extension by PAP. PABII contains an RNP-binding domain and one PABII protein can bind 10-20 As.

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