The document summarizes the tryptophan (trp) operon in E. coli, which contains 5 structural genes that encode enzymes for the production of tryptophan. The trp operon is regulated by a repressor gene and uses two mechanisms of regulation - repression and attenuation. In attenuation, the leader region of the operon can form different stem-loop structures during translation that determine whether transcription will terminate or continue through the structural genes.

1. TRYPTOPHAN OPERON
BY
A.SHASHANKA

2. INTRODUCTION:
• The trp operon is a operon that encodes for the components for the production of tryptophan
• This trp operon is seen in many bacteria, but first characterized in E.coli
• The operon is regulated by regulatory gene
• The trp operon is called Repressive operon

3. Structure of operon:
• Operon has promoter(P), operator(O), leader(trp L) and structural genes.
• Trp operon consists of 5 structural genes. Each gene is responsible for production of different
enzymes. They are as follows:
trp operon gene Gene function
P Genes are used for mRNA creation
O Segment of DNA repressor binds
Trp L Leader sequence & Attenuator sequence is found in
leader
Trp E Gene for Anthranilate synthetase
Trp D Gene for Anthranilate synthetase
Trp C Gene for glycerol phosphate synthetase
Trp B Gene for tryptophan synthetase β
Trp A Gene for tryptophan synthetase α

4. Mechanisms of operon:
• Repression
• Attenuation

5. REPRESSION:

6. ATTENUATION:
• The process of attenuation takes place in Leader region.
• This leader region consists of 4 segments. Each segment has its own function.
o Segment 1 – contains 2 trp coding residues
o Segments 2 & 3 – paired to form stem loop which is Anti terminator
o Segment 3 & 4 – paired to form Terminator stem loop
• The process of translation is depend upon stem loop structure