Lecture 13: Coupling of transcription and translation Flashcards
What is the stringent repsonse?
A response to nutrient starvation - in this case, amino acids.
Translation machinery is downregulated, and amino acid biosynthesis is upregulated.
Explain how the stringent response works.
During starvation, amino acetylated tRNAs are not charged with amino acids. After loading onto the ribosome, this is detected, and translation stops and RelA is recruited.
What is the pathway of RelA within the stringent response?
RelA associates to stalled ribosome via L11, and converts GTP + ATP –> ppGpp.
The protein SpoT then is able to degrade the ppGpp to Gpp + PPi.
Explain how ppGpp affects RNAP.
ppGpp is an alarmone - a second messenger molecule from ribosomes to RNAP.
It binds between the core and shelf, not the active site.
This causes stringent promoters to be downregulated, while relaxed promoters stay the same.
This altered gene expression induces amino acid biosynthesis.
Explain the negative and positive control of RNAP with ppGpp.
Negative control: ppGpp destabilizes the open complex due to the discriminator.
Positive regulation: With high ppGpp, RNAP is released from stringent promoters, so there is a high availability of RNAP for relaxed promoters for amino acid biosynthesis.
Explain transcription polarity.
ORFs downstream of a nonsense mutation will not be expressed. As ‘naked’ mRNA will recruit rho and transcription will be terminated.
Explain the experiment showing that translation elongation rates reduce transcription elongation rates.
Different strains of bacteria were tested under normal and inhibited conditions.
Cm, chloramphenicol is a translation elongation inhibitor
CH184 is a ribosome mutant E. coli strain (rpsL) with slow translation elongation rates
The ratio between transcription and translation rates remains
constant at 3 nt/aa
The yield of transcription meets the need of translation
How is transcription-translation coupled?
Transcription-Translation coupling occurs via physical interactions.
What structure couples the ribosome and RNAP?
Transcription elongation factor NusG couples RNAP and 30S ribosome physically.
NusA mediates elongation and termination, stabilizing the interaction between RNAP and ribosomes.
What is the RNAP response to translation inhibitors in archea?
Translation inhibition redistributes RNAP genome-wide < 5 minutes.
Changes only seen on protein-coding genes indicative of TTC
The addition of an inhibitor decreases the escape efficiency of protein-coding genes.
What is the mechanistic basis for elongation inhibtion?
Mutual exclusive binding of aCPSF1 and
ribosome to RNAP elongation complex Spt5-KOW domain.
Balance between premature termination (PT)
and antitermination (AT) adjusts promoter
strength (aCPSF1 and ribosome respectively).
