BGM1002/L16 Gene Expression in E. coli

Question 1

What antibiotics target the bacterial expression machinery? (2)

Answer 1

Rifampicin
Streptolydigin
Lipiarmycin
CEM-101

Question 2

Define transcription.

Answer 2

Transfer of genetic information from dsDNA to ssRNA (mRNA).

Question 3

Which strand is used as a template for production of mRNA?

Answer 3

Antisense/ template strand

Question 4

Where is the promoter sequence in E. coli?

Answer 4

Immediately upstream of the transcribed region

Question 5

Why is bacterial mRNA described as polycistronic?

Answer 5

It encodes more than one protein

Question 6

How is expression of a group of genes co-ordinated in E. coli?

Answer 6

Through polycistronic mRNA

Question 7

Name the 2 consensus sequences in a promoter sequence.

Answer 7

-35 and -10

Question 8

How many base pairs upstream of the taxon start site is the binding site for RNA polymerase?

Answer 8

40-60

Question 9

What dictates the strength of the promoter sequence?

Answer 9

The similarity of the promoter sequence to the consensus sequence
TTGACA and TATAAT

Question 10

What does the strength of the promoter sequence determine?

Answer 10

The amount of protein produced

Question 11

What are the consensus promoter sequences for E. coli?

Answer 11

TTGACA and TATAAT

Question 12

What ion does RNA polymerase depend on?

Answer 12

Mg2+

Question 13

Name the 5 subunits of core RNA polymerase.

Answer 13

2 alpha
1 beta
1 beta’
1 omega

Question 14

What is the core RNA polymerase with a bound sigma factor called?

Answer 14

Holoenzyme

Question 15

What does core RNA polymerase need to recognise and bind the promoter sequence?

Answer 15

Sigma factor

Question 16

When does sigma factor unbind from RNA polymerase?

Answer 16

Once bound to promoter sequence

Question 17

What is the main sigma factor?

Answer 17

Sigma 70

Question 18

Name 3 alternative sigma factors.

Answer 18

Sigma S - stationary phase
Sigma E - envelope stress
Sigma F - flagellar regulation
Sigma N - nitrogen assimilation
Sigma H - heat shock
Sigma Fecl - iron metabolism

Question 19

What is the main difference between RNA and DNA polymerase?

Answer 19

RNA polymerase does not need a primer to initiate transcription

Question 20

What ion is RNA polymerase dependent on?

Answer 20

Mg2+

Question 21

Describe the difference in exonuclease activity between RNA and DNA polymerase.

Answer 21

RNA polymerase has no proofreading exonuclease activity

Question 22

What is the rate of transcription in E. coli?

Answer 22

20-50nt per sec

Question 23

What is the error rate of RNA polymerase?

Answer 23

1 in 10,000

Question 24

Name the 2 types of termination.

Answer 24

Factor independent
Rho dependent

Question 25

Name 2 common factors of independent terminators.

Answer 25

Series of 4-10 consecutive A-T base pairs
G+C rich region with palindromic sequence that immediately precedes

Question 26

What structure does a palindromic sequence form in mRNA?

Answer 26

Hairpin

Question 27

How does formation of a hairpin loop drive termination?

Answer 27

Disfavours RNA polymerase transcription (pauses transcription)
Weakens H-bonds between transcript and DNA

Question 28

Describe the structure of Rho factor.

Answer 28

6 identical subunits

Question 29

What powers Rho factor?

Answer 29

ATP

Question 30

What is the function of Rho factor?

Answer 30

Helicase
Unwinds RNA-DNA and RNA-RNA duplexes

Question 31

Describe how Rho works. (4)

Answer 31

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