Question

In the Trp operon of bacteria, if the concentration of Tryptophan is high, then

• A. Attenuator shows green signal for the transcription of tryptophan structural genes
• B. Attenuator facilitates elongation step of transcription
• C. Attenuator restricts transcription
• D. All of the above

Answer 1

The correct option is C Attenuator restricts transcription

Tryptophan operon is responsible for the synthesis of amino acid Tryptophan. In E. coli these enzymes are translated from a single polycistronic mRNA. Next to the enzyme coding sequences in the DNA are a promoter, an operator, and two regions called the leader and the attenuator. When the level of tryptophan is low in the cell RNA polymerase reads through the attenuator and genes are transcribed. When levels of tryptophan are high, attenuation causes RNA polymerase to stop prematurely when it is transcribing the trp operon. Only a short, stubby mRNA is made, one that does not encode any tryptophan biosynthesis enzymes.