Which of the following is an example of positive gene regulation?

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The tryptophan gene, in which the presence of tryptophan functions as a co-repressor to prevent its own transcription

The lac gene, in which the repressor prevents the synthesis of the enzyme that degrades lactose, is deactivated by the presence of lactose.

CAP, which acts as a required transcription factor for the enzymes that degrade lactose.

All of the above.

answer is A.

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Detailed Solution

Concept: A protein or activator must bind to start transcription in positive gene regulation. The operon will become inactive when the positive regulatory protein is missing or inactive.
When the end product tryptophan is present in sufficient amounts, its molecules act as co-repressors, and the tryptophan combines with the inactive repressor to form the active trp repressor, which then binds to the operator and prevents the transcription of the operon. The tryptophan is composed of repressible Operon, which contains five structural genes (trp E, D, C, B, and A). Positive regulation or feedback repression is the term used for this.
Hence, option 1 is the correct answer.

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