The tryptophan (trp) operon in E. coli contains 5 structural genes (trpE, trpD, trpC, trpB, trpA) that encode enzymes for the biosynthesis of tryptophan from chorismate. These genes are regulated by a repressor protein that binds to the operator region between the promoter and first structural gene. When tryptophan is present, it binds to the repressor, causing it to bind to the operator and repress transcription. When tryptophan is absent, transcription occurs. An additional level of control is provided by a leader sequence between the promoter and first structural gene.

1. TRP OPERON
Dr. P. Suganya
Assistant Professor
Sri Kaliswari College (Autonomous)
Sivakasi

2. OPERN An operon is a group of closely linker
structural genes and associated control
genes which regulate the genetically
controlled metabolic activity.
SRTUCTURE
OF
TRP
OPERON
Tryptophan operon is E.coli is response for the biosynthesis
Of tryptophan amino acids is the cell from the initial
precursor Chorisinic acid the synthesis of amino acid
tryptophan is carried Out by 5 enzyme.
STRUCTURAL
GENES
The genes encoding there enzyme are form
adjacent to one another is succession and the
named are as Trp E, Trp D, Trp C, Trp B and Trp A
The genes Trp E is the first to be translated.

3. PR Trp Ptrp O L TrpE TrpD TrpC TrpB TrpA
DNA
Promoter For
Repressor Repressor Gene
Promoter
Operator
Leader sequence
Trp Operon

4. Chorisinic Acid
Anthranilate synthase
Trp E
Anthranilic acids
Anthranilate synthase II
Trp B
Phosphorinyl anthrosnitic Acid
Trp C
Carbonyl Phenyl Amino 1 – Deoxyribose Phosphate
Indole 3 – glycerol (1) synthase
Indole 3 – glycerol 5
Tryptophan
Tryptophan synthesis
Trp B
Trp A

5. CONTOL OR REGULATORY GENES
 These control the activity of structure genes either by induction as suppression.
PROMOTER GENES
 Is a segment of DNA at which RNA Polymerase binds and initiate the
transcription of the structure genes.
OPERATOR GENES
 Is a segment of DNA at which the polymerase binds to it and control the
Transcription of form structure gives.

6. LEADER GENES
Trp has a regulatory site present between promoter/operator and the first structure
Genes Trp E called Leader Sequences. Which is transcript into mRNA. which is
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7. REGULATIONMECHANISMS OF TRYPHTOPHAN OPERON IN E.coli
PR Trp Ptrp O L TrpE TrpD TrpC TrpB TrpA
DNA
Promoter For
Repressor Repressor Gene
Promoter
Operator
Leader sequence
mRNA
TrpR
5’
3’
P
Inactive Form Of repressor Protein
Active Form Of Repressor
Negative Regulator
T
B
Presence Of Trp Operon

8. EVENTS
When The Trp present tryptophan binds to the repressor molecules the activated
repressor Binds to the operator and the trp operon is repressor.

9. PR Trp Ptrp O L TrpE TrpD TrpC TrpB TrpA
DNA
Promoter For
Repressor Repressor Gene
Promoter
Operator
Leader sequence
3’
5’
TrpR - mRNA
Inactive Form Of Repressor
RNA Polymerase
3’
5’
L E D C B
Leader Peptide
Anthranilate synthase I
Anthranilate Synthase II
Tryptophan Synthase B Protein
Tryptophan
Synthase
Protein

10. EVENTS
 When the tryptophan in absolute
 Repressor solved Binds To Operator
 Operon activity transcribes mRNA
ALTERATION
 The important element of the Trp operon the leader sequence which is
160bp in size , control The expression of the trp operon through a process
called alternation this sequence has 4 domain.

11. FUNCTION OF THE GENES
Trp Operon Genes Genes Function
P/O Promoter , Operator sequence Is found In The
Promoter
Trp L Leader sequence Alternator (A) Sequence Found In
The Leader
Trp E Operons For The Anthranilate Synthesis subunit I
Trp D Genes For Anthranilate synthesis Subunit II
Trp C Genes To Indole Glycerol Phosphate synthesis
Trp B Operon For Tryptophan Synthesis Subunit B
Trp A Genes For Tryptophan Synthesis Subunit Alpha

12. THANK YOU