BGM1002/L16 Gene Expression in E. coli Flashcards
What antibiotics target the bacterial expression machinery? (2)
Rifampicin
Streptolydigin
Lipiarmycin
CEM-101
Define transcription.
Transfer of genetic information from dsDNA to ssRNA (mRNA).
Which strand is used as a template for production of mRNA?
Antisense/ template strand
Where is the promoter sequence in E. coli?
Immediately upstream of the transcribed region
Why is bacterial mRNA described as polycistronic?
It encodes more than one protein
How is expression of a group of genes co-ordinated in E. coli?
Through polycistronic mRNA
Name the 2 consensus sequences in a promoter sequence.
-35 and -10
How many base pairs upstream of the taxon start site is the binding site for RNA polymerase?
40-60
What dictates the strength of the promoter sequence?
The similarity of the promoter sequence to the consensus sequence
TTGACA and TATAAT
What does the strength of the promoter sequence determine?
The amount of protein produced
What are the consensus promoter sequences for E. coli?
TTGACA and TATAAT
What ion does RNA polymerase depend on?
Mg2+
Name the 5 subunits of core RNA polymerase.
2 alpha
1 beta
1 beta’
1 omega
What is the core RNA polymerase with a bound sigma factor called?
Holoenzyme
What does core RNA polymerase need to recognise and bind the promoter sequence?
Sigma factor
When does sigma factor unbind from RNA polymerase?
Once bound to promoter sequence
What is the main sigma factor?
Sigma 70
Name 3 alternative sigma factors.
Sigma S - stationary phase
Sigma E - envelope stress
Sigma F - flagellar regulation
Sigma N - nitrogen assimilation
Sigma H - heat shock
Sigma Fecl - iron metabolism
What is the main difference between RNA and DNA polymerase?
RNA polymerase does not need a primer to initiate transcription
What ion is RNA polymerase dependent on?
Mg2+
Describe the difference in exonuclease activity between RNA and DNA polymerase.
RNA polymerase has no proofreading exonuclease activity
What is the rate of transcription in E. coli?
20-50nt per sec
What is the error rate of RNA polymerase?
1 in 10,000
Name the 2 types of termination.
Factor independent
Rho dependent
Name 2 common factors of independent terminators.
Series of 4-10 consecutive A-T base pairs
G+C rich region with palindromic sequence that immediately precedes
What structure does a palindromic sequence form in mRNA?
Hairpin
How does formation of a hairpin loop drive termination?
Disfavours RNA polymerase transcription (pauses transcription)
Weakens H-bonds between transcript and DNA
Describe the structure of Rho factor.
6 identical subunits
What powers Rho factor?
ATP
What is the function of Rho factor?
Helicase
Unwinds RNA-DNA and RNA-RNA duplexes
Describe how Rho works. (4)
Loads onto C-rich sequences (Rho Utilisation Sites- RUT)
RNA polymerase pauses at ter site
Rho unwinds RNA-DNA hybrid
RNA pol, mRNA and Rho released
