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3’ Tailing
3’ Tailing
At their 3' end, most eukaryotic mRNAs have a string of 80 to 250A residues , making up
the poly(A) tail
...
Importance: The poly (A) tail and its associated proteins probably help protect mRNA from
enzymatic destruction
...
The poly(A) tail is added in a multistep process
...
The mRNA site where cleavage occurs is marked by two sequence elements: the
highly conserved sequence (5')AAUAAA(3'), 10 to 30 nucleotides on the 5' side (upstream) of
the cleavage site, and a less well-defined sequence rich in G and U residues, 20 to 40 nucleotides
downstream of the cleavage site
...
This enzyme does not require a template but
does require the cleaved mRNA as a primer
...
Pol II synthesize the RNA beyond the
segment of transcript containing the
cleavage signal sequence ,including the
highly conserved upstream sequence
(5’)AAUAAA
...
2
...
The rna is cleaved by the endonuclease
at the point 10 to 30 nucleotides 3’ to
the sequence AAUAAA
...
The
polyadenylate
polymerase
Figure 1: Addition of poly (A) tail to the primary Rna transcrip
3’ Tailing
synthesize a poly (A)tail 80 to 250 nucleotides long, beging at the cleavage
site
...
This editing includes processes that add or delete bases in the coding regions of
primary transcripts or that change the sequence (By for example enzymatic deamination of a C
residue to create a U residue)
...