So now we need to look at little bit at
eukaryotes and how things are different.
Now, I mentioned earlier that there
was only one RNA polymerase.
I did lie a little bit.
There are three that we know
about now in eukaryotes.
One of them is a polymerase.
One, which is involved in
making ribosomal RNAs.
We don’t need to worry about those here.
The other one is a polymerase III
that is involved in making tRNA.
And I introduced you to
those in the last lecture.
And finally, the one that we really care
about is the eukaryotic RNA polymerase
that’s involved in making messenger RNA in
eukaryotes, is called RNA polymerase II.
It is also involved in making
some of the nuclear RNAs,
but primarily, we are
looking at it for the
purposes if transcription
in eukaryotic cells.
So let’s see about some changes
that we might see in transcription
in eukaryotic cells.
Naturally, it’s going to be
a little bit more complex.
And once again, we don’t
necessarily know as much
about it as we know about
it in prokaryotic cells.
We do know that we begin
with the binding of a
transcription factor to
the promoter regions.
So these transcription factors are
going to help our RNA polymerase II
bind to the promoter region
and begin transcription.
Each of them, we
do have names for.
I’m going to spare you the suffering of
learning which ones arrive when and how.
But either way, a bunch if
transcription factors help
everything assemble properly
on the eukaryotic DNA strand.
So these other transcription factors
aid in getting the whole thing going.
The point here though
is these are all points
at which we could
regulate gene expression.
We need all of these transcription
factors to get going.
If something’s absent,
we’re not going to have transcription or
maybe we’ll have it happen more slowly.
But once all the transcription
factors are assembled,
then we know that RNA polymerase II can
join the game and initiate transcription.
So we form an initiation complex
with the RNA polymerase
and the transcription factors
and we’re good to go.
Now, one additional note,
we are now learning that in addition
to all the transcription factors,
there are some
And polymerase II will often very
close to the initiation site
or the transcription start
site, will very often pause
and it’s only with these
other proteins, that come into
play this transcription game,
that we can push the polymerase
further down the strand
and get it going with the
process of transcription.
Otherwise, it will just
hang out there and pause.
So more potential for regulation
of gene expression in eukaryotes
because of all of the extra
players that are also proteins
that are also coded on DNA
and need to be transcribed and translated
in order to get the whole thing going.
You’ll recall there are many
mechanisms of cell communication
and all of those
come into play here.
So it really could get