Transcription And RNA Processing 1 Flashcards
What are housekeeping genes?
Genes that are needed for cell function (structure and metabolism)
Constitutive expression (same in all cells)
What are tissue-specific genes?
Cell type specific proteins
Highly regulated
What is similar between the 3 RNA polymerases?
Share 9 core subunits
Require general transcription factors to initiate transcription
What does RNA pol I transcribe?
The precursor of large ribosomal rRNAs.
18S, 28S, 5.8S
What does RNA pol II transcribe?
All mRNA genes as well as microRNA precursors and most snRNA involved in splicing
What does RNA pol III transcribe?
Small genes like tRNAs, U6 snRNA, and the 5S rRNA gene
What is a promotor and what elements make it up?
DNA region where the enzyme required for transcription binds.
TATAA box
Inr (initiator) elements
BRE - TFIIB recognition element
Downstream elements
What is the role of TFIID?
First step in transcription.
Binds the TATA box via TBP.
15 protein complex with TBP and TAF’s
(TBP associated factors)
What is the role of TFIIB?
Binds to the TFIID complex via TBP and to the BRE region on the DNA
What TF does RNA pol II bind with prior to attaching to the transcription initiation complex?
TFIIF
What does the RNA PolII-TFIIF complex bind to?
The TFIID-TFIIB complex that is already attached to the DNA
What are the final two factors to bind to the transcription initiation complex?
TFIIE and TFIIH
Which TF has enzymatic activity and what is the activity?
TFIIH
Helicase
Kinase
What even initiates transcription?
The phosphorylation of the 5th serine residue in a repeated amino acid sequence by TFIIH on the C-terminal domain of RNA Pol2.
Leads to dissociation of Pol2 from the complex.
What is the function of Mediator protein?
Interacts with GTFs and RNA Pol II and helps regulated transcription initiation
Loses affinity for the complex whe the CTD of RNA Pol is phosphorylated
What is the holoenzyme model of transcription initiation?
The RNA pol enzyme forms a complex with GTFs before binding the promotor.
The complex is recruited to specific promoters by activation factors.
What is the role of HATs and HDACs?
Control the amount of condensation of chromatin via acetylation
Acetylated = active chromatin
Deacetylated = inactive chromatin
How is rRNA produced?
Initially transcribed by RNA Pol I as a 45S transcript.
Processing forms 28S, 18S, and t.8S rRNA’s
Where are the 5S and tRNA promoters located?
Downstream of the transcription start site
What combination of TFs is used in 5S rRNA transcription?
TFIIIB, TFIIIC, and TFIIIA
What combination of TFs is utilized in tRNA transcription?
TFIIIB and TFIIIC
What TFs are used in U6 mRNA transcription?
TFIIIB, and SNAP
What are snoRNPs and what is their function?
Molecules of snoRNA and protein that participate in rRNA processing
Guides nucleases to specific sites in pre-rRNA
Can also cause base changes (uridine to pseudouridines)
What is RNAse P and what is its function?
RNAse P is an RNA and protein complex that processes the 5’ end of pre-tRNAs.
The RNA is the catalytic component
What is responsible for cleaving the 3’ end of a tRNA during processing?
A conventional protein RNAse.
What is added or encoded to the 3’ end of a tRNA?
A CCA sequence for amino attachment.
Why are bases modified in the tRNA structure?
They change the H-bonding capability of the base pairs and stabilize hairpin loops
What are the four components of rRNA processing?
Cleavage reactions
Linkage through H-bonding
Methylation of bases and sugar residues
Chemical conversions of bases
What are the three components of tRNA processing?
Cleavages at the 3’ end and 5’ end
Attachment of CCA bases
Replacement or modification of standard RNA bases
