Understanding Eukaryotic Transcription: A Comprehensive Overview

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 initiation of transcription 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 function of transcription factor 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 and TF to be

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 polymerase 2 on the promoter

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 DNA outside the promoter next transcription factor tf2 e binds

the pre-initiation complex 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 pre-initiation complex to open complex

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

the helicopter 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

phosphorylation stimulates elongation 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 be slow 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 prime direction 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 tri phosphatase 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 of translation

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 c-terminal domain of RNA polymerase 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 prevents degradation of poly a tail [Music]