Prokaryotic transcription ; RNAP + σ factors ; Sigma factors

1. Transcription
Presented ,
Mr-Pradeep D Devkate
M.Sc Microbiology, B.Ed, MH-SET, 2-GATE(Biochemistry, Zoology,
Botany) , Ph.D. pursing .

2. Holoenzyme = RNAP + σ factors
• In a Bacteria single RNA Polymerase which are interact with different
σ- factors - activation of different gene ..
Initiation factor σ factors ..
Nif gene

3. Terminator Sequence
Start site
5’
3’
3’
5’
-10bpSequence(6bp)=TATAAT
-35bpSequence(6bp)=TTGACG
Spacer Sequence- Are not conserved
Spacer sq
Conserved sequence More similar
Upstream Downstream
Upstream – In upstream sequence - Promoter , Operator (Regulatory sequence)
Downstream-- In Downstream sequence - Coding sequence, Terminator Sequence

4. Eukaryotic RNA polymerase: I,II,III,IV,V
• Multiple RNA polymerase and each composed of 10 or more subunits.
• Five of them have homology with bacterial RNA polymerase.
1) RNA polymerase I : It transcribe rRNA genes
28 s rRNA , 5.8 s rRNA, 18 s rRNA ( Nucleolus)
2) RNA polymerase II: It transcribe mRNA, mi-RNA block translation ),
SnRNA(splicing of pre RNA) (Nucleus)

5. 3) RNA polymerase III: It transcribe tRNA genes , ssRNA , U6 SnRNA
(Nucleus)
4) RNA polymerase IV: It transcribe SiRNA in plant system only
s(Nucleus)
5) RNA polymerase V: It transcribe SiRNA in plant system only (Nucleus)

6. Inhibitors of RNA polymerase :
1) α Amintin: isolated from poisonous mushroom called Amentia
Phallodiae.
 Also called as Death cap mushroom or Angel of death.
It strongly inhibits the RNA polymerase II and Moderately inhibit to
RNA polymerase III .
Sensitivity of α-Amintin =RNA pol II > RNA pol III > RNA Pol I

7. Eukaryotic Promoter :

8. Eukaryotic Transcription Initiation :
• for Initiation of transcription require many proteins like
GIFs = Generalised transcription factors.
1) Firstly TF-II D binds on TATA box
( 11 subunit protein )
2) One TBP (TATA binding protein) and 10 TAFs (TATA associated factors )
 TBP is β Sheet structure motif interact with minor groove of DNA
 Generally proteins which interact with DNA are with helix-turn-helix
motifs and interact with major groove of DNA.
 But Transcription Factor II D uses β Sheet structure and interact with
minor groove of DNA .

10. • β Sheet structure breaks hydrogen bonding of dsDNA into ssDNA.
• TF-II D stabilizes the interaction.
• TF- IIA comes and join ssDNA
TF II B bind on BRE ( B response Element )
After that TF II F brings RNA pol II
TF II F has CTD tail ( carboxy terminal domain) which consists of Hepta-speptide
sequence (7 amino acids ) (Tyr-Ser-Pro-thr-ser-pro-ser)
TF II E and TFII H recruits on RNA pol II
TF II H has kinase activity(Initiation) and helicase activity (Elongation)

11. • TF-II-D = TATA Box or DNA Binding Domain , Bind to minor groove “bent”
DNA 80..and initiate the transcription.
• TF-II-A= stabilized to TF-II-D
• TF-II-B = Protein-Protein Interaction ; DNA protein interaction.
it binds to TF-II-D , TF-II-F
• TF-II-H= Helicase Activity
• One subunit Kinase activity on α-CTD of Polymerase
• DNA Repair process
• Also activate to 5’ capping enzymes .
• TF-II-S = hydrolytic editing of RNA polymerase ( Gre like activity)