CSB349H1 Lecture Notes - Lecture 10: Cleavage And Polyadenylation Specificity Factor, Flight Instructor, Consensus Sequence
14 May 2018
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Lecture 10: mRNA Processing
Transcription Termination:
• RNAPII generate the mRNA and has a CTD that will be phosphorylated and recruit specific
proteins required for transcribing and processing mRNA
o Transcription is terminated when RNA is cleaved by endonuclease and a poly(A)
tail is added to the exposed 3’ end
§ *Poly(A) tail is not in-coded in the sequence; it is added after cleave of mRNA
o CPSF – cleavage and ploy-adenylation specificity factor
o CstF – cleavage stimulating factor
ð There is no stop signal for transcription – RNAPII will continue to transcribe even after the
mRNA is released for a few base-pairs and will eventually stop because factors will be
dissociating from the CTD
Cleavage/Poly-Adenylation Complex:
• All eukaryotic mRNA are polyadenylated – exceptions: histone mRNA snRNA, rRNA, tRNA
o mRNA a consensus sequence:
(1) AAUAAA [15bp upstream of cleavage site] | (2) G/U rich [50bp downstream]
ð CPSF is a large 3-subunit protein that forms a complex with the AAUAA sequence and is
stabilized via binding of:
o CstF – interact with G/U rich sequence
o CFI & CFII [cleavage factor] – help stabilize protein-RNA complex
o PAP [poly-A-polymerase] – binds to complex before cleavage occurs
§ mRNA cannot be unprotected hence PAP binds prior to cleavage
PABPII:
• PABPII facilitates polyadenylation via PAP – adds 250 A residues
• PABPII also signals PAP to terminate addition of A after adding 250
Assembly of Complex:
• CPSF will recognize the sequence AAUAAA on the mRNA and bind to it leading to the
recruitment of the other proteins that will function in cleaving the mRNA
o PAP will begin adding A to the mRNA facilitated by PABPII
