RNA Polyadenylation

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RNA Polyadenylation
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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.
• Adapted from Textbook Molecular Cell Biology
  Lodish H., Berk A., Zipursky L.,Matsudaira P.,
  Baltimore D. and Darnell J.