L5 Trp Operon

Question 1

Attenuation

Answer 1

• Regulation gene expression through early transcription termination
• For Attenuation:
  Trans-acting regulatory protein = ribosome
  Positive regulator
• Attenuation used in translation to effect the level of transcription
• Attenuation regulates a number of aa biosynthetic genes

Question 2

Trp operon regulated by two mechanisms

Answer 2

1. TrpR

2. Attenuation

Question 3

Trp operon cis acting deletion

Answer 3

LD102
ED53
Both deletion mutants are trp- pheno.
independent to repression of Trp by TrpR

Question 4

Leader Sequence

Answer 4

• contain short ORF and a terminator
• Capacity to synthesise a short leader peptide
• Sequence with the capacity to form a terminator sequence (stem loop structure)
• Contains 4 sequences upstream to TrpE:
  The four sequences can form stem&loop structures depending on its complementation to other sequences

Question 5

Trans-acting mutations

Answer 5

TrpT, TrpX, TrpS
all increase trp operon expression in TrpR- background
These mutants effect the same pathway as the LD102 deletion (attenuation)

Question 6

What do TrpT, TrpX, TrpS code for?

Answer 6

OneNote

Question 7

Leader peptide

Answer 7

• contains two Trp codon

Question 8

Leader Sequence Stem&Loop structures

Answer 8

1w/2 & 3w/4
OR
2w/3 (1 does not pair with 4)

Question 9

3:4 structure

Answer 9

• form terminator hair pin
• factor independent transcription terminator
• formed when there is high trp levels
  => transcription termination

Question 10

2:3 structure

Answer 10

• in 2:3, the terminator region is SS
• formed when trp level is low
• ribosome pauses at trp codon in leader sequence of mRNA during translation of leader sequence
  => no transcription termination

Question 11

Bacillus subtilis - Trp Operon

Answer 11

- similar structural genes 
BUT 
- regulated differently:
no TrpR
Different attenuation

Question 12

B.subtilis - leader region

Answer 12

• A,B,C,D region
• no peptide translated
• low trp levels = A:B stem loop structure
• high trp levels = C:D stem loop structure => transcription termination

Question 13

TRAP protein

Answer 13

Trp RNA-binding attenuation protein

• binds to trp, forms 11 subunit complex => binds to mRNA, allows terminator to form => RNA pol terminates
• each subunit of TRAP binds to UAG/GAG triplet in mRNA, forming stable protein-RNA complex
• Negative regulatory protein
• Repressible by trp

Question 14

antiTRAP protein

Answer 14

• antiTRAP protein binds to and inactivates TRAP
• high trp (no uncharged trp tRNA to bind to antiTRAP mRNA = terminator stem and loop forms) => no antiTRAP gene exp => TRAP protein expressed
• low trp (uncharged trp tRNA present to bind to antiTRAP mRNA = no terminator stem and loop forms) => antiTRAP gene exp => TRAP protein not expressed