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?