Suppose an operon has the following characteristics: (1) The operon codes for st

Question

Suppose an operon has the following characteristics: (1) The operon codes for structural proteins that convert compound Q to compound B. (2) The operon is controlled by a constitutively expressed regulatory gene called reg. (3) In wild-type individuals, the operon is transcribed in the absence of compound B but not in the presence of compound B. (4) In reg- mutants, the operon is constitutively transcribed. Is this operon inducible or repressible? Why?

Suppose an operon has the following characteristics: (1) The operon codes for structural proteins that convert compound Qto compound B. (2) The operon is controlied by a constitutively expressed regulatory gene called reg. (3) In wild-type individuals, the operon is transcribed in the absence of compound B but not in the presence of compound B. (4) in reg mutants, the operon is constitutively transcribed. Is this operon inducible or repressible? Why? O It is inducible because wild-type transcription does not occur in the presence of compound B. O t is inducible because the operator in reg mutants can still bind to compound B O It cannot be determined because the number of structural genes is unknown. O t is repressible because reg transcription only occurs in the presence of compound B O t is repressible because wild-type transcription is repressed in the presence of compound B

Explanation / Answer

Answer: (e) It is repressible because wild-type transcription is repressed in the presence of compound B.

Explanation:

Because the operon is transcriptionally inactive in the presence of compound B, the regulatory gene reg most likely codes for a repressor protein that requires compound B as a corepressor.

The data suggest that the operon is repressible because it is inactive in the presence of compound B, but active when compound B is absent

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