0:00
The focus of this presentation
is Nuclear Pre-mRNA Splicing.
Splicing is an essential
step in the expression
of almost all genes
and higher eukaryotes.
We will begin by discussing
the phenomenon of splicing
and then discuss the
mechanism by which it occurs.
We will then shift to a discussion
of how splicing, specifically
alternative splicing, contributes
to proteomic diversity.
Finally, we will briefly discuss
the role of splicing in messenger
RNA surveillance
and quality control.
0:32
This slide illustrates the
structure of a typical higher
eukaryotic protein coding gene.
The transcribed region is
shown in green and yellow,
and the flanking regions
are shown in red.
The actual coding sequence,
comprised of multiple exons,
is shown in dark green.
This sequence is interrupted by
multiple intervening sequences,
or introns, which
are shown in yellow.
Upon transcription, a
pre-mRNA is produced which
contains all of the
exons and introns.
To produce a functional
messenger RNA,
the introns must be
removed by splicing,
and the exons must be
fused together in the order
in which they were transcribed.
1:14
Here is a representation of
a typical pre-mRNA intron.
The intron contains three
important sequence elements.
Two of these elements, the five
prime and three prime splice sites,
define the boundaries of the intron.
The third element, which resides
just upstream of the three
prime splice site, is
called the branch point.
As we will see in a
moment, the branch point
is essential for the
chemistry of splicing.
Comparison of the sequences
of many thousands of introns
has revealed that each of the
three important intronic sites
is characterized by
a consensus sequence.
However, with the exception of
the first and last two nucleotides
of the intron in the branch point
itself, which are nearly invariant,
considerable variation is
allowed at all three sites.
We will come back
to this variability
in splicing signals later.
