Question

A mutation that renders the regulatory gene of a repressible operon nonfunctional would result in

• A. excessive synthesis of a catabolic activator protein
• B. irreversible binding of the repressor to the promoter
• C. inhibition of transcription of the structural genes
• D. continuous transcription of the structural genes

Answer 1

The correct option is D continuous transcription of the structural genes

In a repressible operon, the operon is normally on and transcription occurs for the synthesis of enzymes. This synthesis of enzymes takes place with the help of the structural genes.

In presence of corepressor (for e.g. tryptophan in trp operon) inactive repressor (aporepressor) gets converted to the active repressor. This active repressor binds to operator region and stops transcription. If any mutation takes place in regulatory genes i.e. those involved in the formation of operator and repressor, operon will never get turned off. This will result in continuous transcription of the structural genes.

So, the correct option is 'continuous transcription of the structural genes'.