Eukaryotic transcription is a complex, multi-step process involving RNA polymerase II and a suite of general transcription factors that regulate gene expression, followed by mRNA processing events like capping and polyadenylation.
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heroin quick back and mister basics here
let's talk about eukaryotic
transcription the enzyme required for
the process of transcription is the RNA
polymerase the prokaryotes have only one
RNA polymerase enzyme while the
eukaryotes held 3 RNA polymerase enzyme
RNA polymerase 2 is a major polymerase
enzyme involved in a transcription of
mRNA in eukaryotes the RNA polymerase 2
along with other proteins known as the
transcription factors are required for
the transcription factors are also known
as general transcription factors
let's see how the transcription factors
are designated the initial two letters
are written as DF which stands for
transcription factor the two indicates
that it's a transcription factor for RNA
polymerase 2 the letter next to 2 can be
a b d e f and h depending on the
because they are so many transcription
factors involved in eukaryotic
transcription it's easy to memorize them
with the help of mnemonics
for example the mnemonics of tf2a is
Apple the F to B is ball tf2d is dog TF
to E is elephant t f2f1 tf2h is helicopter
let's see function of each of them in
the first step of initiation of
transcription the transcription factor
EF do be binds the tata element in the promoter
the eukaryotic promoter is about 40
nucleotides long and located upstream
and downstream of the transcription
start site
about 30 nucleotides upstream to the
start site there's an 80 rich sequence
known as the Tata box or data element
tf2d has a protein called TBB which
binds data sequence tbp is also known as
starter binding protein once TPP binds
Tata sequence it bends the DNA by 80
degrees this bending of DNA further
helps in the binding of other
transcription factors this includes tf2a
tf2a tf2a helps in stabilizing the
binding of tf2d with the promoter
tf2b interacts with tbp and the promoter
region downstream to the data sequence
tf2b helps in the recruitment of RNA
now the RNA polymerase cannot bind the
promoter on its own
a transcription factor D f2f RNA
polymerase 2 to bind the promoter d f2
f3 and TF to be while recruiting the RNA polymerase
D F to F of n RNA polymerase to contact
next transcription factor tf2 e binds
tf2 II helps in the binding of other
transcription factor tf2h tf2h is a very
large complex with total nine subunits
are of nine two subunits help ATPase
activity using energy from ATP it acts
like a helicase and melts the promoter
and this finally causes transition from
the remaining seven subunits of tf2h has
a kinase activity this kinase activity
phosphorylates the c-terminal domain or
the tail of RNA polymerase 2 leading to
promoter escape and transcription elongation
so we can remember the events of
transcription initiation with the
following mnemonics the dog eats the
Apple and plays with the football he
gets tired and sits in front of the fan
when he sees an elephant he runs away in
transcription elongation once RNA
polymerase help initiated transcription
it shifts into elongation phase the
transcription factors that helps in
elongation are called elongation factors
there are two such elongation factors d
fe b and d f2 s TF EB is recruited to
polymerase by transcription activators
TF EB is a kinase protein and
phosphorylates serine residues in the
c-terminal domain of the polymerase this
the other factor involved in elongation
is tf2 s now the rate at which the RNA
polymerase transcribes to DNA is not
same at all DNA sequences at some DNA
sequences the rate of transcription is
fast while at other DNA sequences it can
tf2 s helps to increase the rate of
transcription at the region where the
rate of transcription becomes slow it
also does not allow RNA polymerase to
pause and encourages to move on 5 -
capping as the RNA polymerase starts
elongation the mRNA starts forming the
formation of mRNA occurs in 5 prime to 3
the first RNA processing
that occurs during elongation is the
fire - capping during this process the
terminal gamma phosphate of the
nucleotide is removed by the enzyme RNA
in the next step gwah neil transferase
enzyme carries out reaction between beta
phosphate of the first nucleotide and
alpha phosphate of gdb once guanine is
attached methyl transferase enzyme
attaches a methyl group to the guanine
nucleotide this structure is called Phi
- cap and it helps in the recruitment of
mRNA on the ribosome for the initiation
termination of transcription when the
RNA polymerase reaches the end of the
gene the c-terminal domain of the RNA
polymerase interacts with two proteins
csdf and cpsf the csdf stands for clear
rate stimulation factor and cpsf stands
for cleavage and polyadenylation
specificity factor when the end of the
gene is transcribed into RNA these
proteins are recruited to the mRNA by
the Quebec stimulation factor cstf
leaves the MRNA once the mRNA is cleaved
csdf dis associates the cps f10 recruits
poly a polymerase which adds about 289
residues at the tree - end giving rise
to poly a tail the poly a polymerase
uses ATP for this purpose
once poly a tail is formed the poly a
binding protein binds to poly a tail and
during the step cpsf is released from
the mRNA the poly a binding protein
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