Hello. My name is Jim Manley.
I'm at Columbia University of New York.
In this section, we'll be talking about the last step in the expression of
a gene which is the Polyadenylation of the newly synthesized mRNA Precursor.
This is a surprisingly complex reaction as we've learned over the last 25 years or so.
And here we'll be talking about the mechanism and regulation of Polyadenylation,
as well as unexpected connections of this reaction with other cellular processes.
This slide is a very old one,
made well before the advent of PowerPoint in approximately 1980, 81,
and it depicts very simply the end of a messenger precursor,
and the reaction that leads to the polyadenylated tail on the messenger RNA.
The top wavy line is the mRNA as it's transcribed by
RNA polymerase two and indicates
two sequence elements known back then to be involved in Polyadenylation.
One is the well-conserved AAUAAA located about 10 to 30 bases upstream
of the site of endonucleolytic cleavage which is indicated by a vertical line.
Downstream is the less well-conserved sequence which is
characterized by GU richness in many but not all mRNAs.
The Polyadenylation reaction involves endonucleolytic cleavage that I just mentioned
followed by poly(A) addition in which the three prime hydroxyl group
generated by the endonucleolytic cleavage serves as a primer for poly(A) polymerase which
synthesizes the tail in invertebrates of about 200 A residues shown on the bottom line.
The region of RNA downstream from the cleavage site is indicated by
a dashed line here because it's rapidly degraded in the cell nucleus following cleavage.
This slide introduces the Polyadenylation machinery.