RNA Polymerases - Lecture 10 Flashcards
What makes up the prokaryotic RNA polymerase?
○ Sigma (σ)
○ 2 x alpha (α)
○ 2 x beta (β + β’)
○ Omega (ω)
What is the sigma unit responsible for?
Recognises the promoter
What are the alpha units responsible for?
Activation of the polymerase and to work under certain conditions and assembly
What are the beta units responsible for?
○ Catalysis
○ Termination
○ Open up DNA and make RNA copy
What is the omega unit responsible for?
○ Assembly
○ Folding
○ Required for some genes
○ Doesn’t do much
What happens when the RNA polymerase begins transcribing?
○ Sigma unit is ejected
○ Core enzyme is competent for elongation
How many RNA polymerases do prokaryotes have?
One
What are the RNA polymerases that eukaryotes have?
○ Pol I
○ Pol II
○ Pol III
What does the Pol I transcribe?
Ribosomal RNA genes (rRNA)
What does Pol II transcribe?
○ Protein coding genes (mRNA)
○ Small Nuclear RNA (snRNA)
○ Needs accessory proteins to bind to DNA
What does Pol III transcribe?
○ transfer RNA (tRNA)
○ rRNA
○ snRNA
What transcription factors are involved in the assembly of RNA polymerase II?
○ TFIID
○ TFIIA
○ TFIIB
What is TFIID?
○ Transcription factor 2
○ Made up of TATA binding proteins (TBP): recognise A-T rich sequences and has a sequence similar to σ
○ Also made up of TBP-Associated Factors (TAFs)
What is TFIIA?
Helps TFIID to bind
What is TFIIB?
Sets distance from TATA element to start site
What does TFIIE, F, H, J, K do?
○ Interacts with DAB complex and recruitment of polymerase II
○ Blocks non-specific binding of polymerase II to DNA
○ Promoter clearance
○ Helicase
○ Processivity and elongation
○ Transcription-coupled DNA repair
How is RNA polymerase I recruited?
○ Upstream control element (UCE) is binded to upstream binding factor (UBF)
○ UBF binds to SL1
○ SL1 recruits RNA pol I
What makes up SL1?
○ TBP
○ Pol-I specific TAFs
How is RNA polymerase III recruited?
○ Promoter is withing coding region
○ Regulatory regions are after transcription start site (A box and B box)
○ TFIIIC binds to B box
○ TFIIIB is recruited upstream of start-site
○ Once transcription is initiated, TFIIIC gets displaced
What makes up TFIIIB?
TBP + 2 pol III specific TAFs
What is different about RNA polymerase III when transcribing 5S rRNA genes?
Use an extra factor TFIIIA to recruit TFIIIC
What is different about RNA polymerase III when transcribing snRNA genes?
○ Upstream promoter
○ TATA box recognised by TBP
