Question

A Lac repressor is a tetramer repressed when bound to the inducer. The trp repressor is a ____________________

(a) Dimer inactivated when bound to the inducer

(b) Dimer activated on inducer binding

(c) Tetramer inactivated on inducer binding

(d) Tetramer activated on inducer binding

I had been asked this question by my school teacher while I was bunking the class.

This is a very interesting question from Operons : Trp topic in division Gene Expression : Transcription Prokaryotes of Cytogenetics

Answer 1

Correct answer is (b) Dimer activated on inducer binding

To explain: A trp repressor is a dimer which can’t bind to the cis element unless it is bound to the inducer tryptophan. Only then it undergoes conformational change such that it then binds to the operator.