1.You have isolated a repressor for an inducible operon and have determined that

Question

1.You have isolated a repressor for an inducible operon and have determined that it has two different
binding sites, one for the inducer and one for the operator. Mutants of the repressor result in 3 different
phenotypes as far as binding is concerned. What are these phenotypes?

2. You have isolated two E. coli mutants that synthesize -galactosidase constitutively.
a) If these mutants affect different functions, in what two functions could they be
defective?
b) You can make a partial diploid of the mutants with the wild-type. What result do you expect
for each mutant?

Explanation / Answer

1. The repressor binds to the inducer and to the operator. So mutants can show these 3 phenotypes: *doesnt bind to the inducer or to the operator *binds to the inducer but not to the operator *binds to the operator but not to the inducer -------------- 2. a) The two functions in which these two mutants could be defective could be: *repressor structure *operator structure b) For the first mutant: the repressor binds only partially to the operator. This does not switch off the production of -galactosidase SEcond mutant: as the normal repressor cannot bind to the abnormal operator, this does not switch off the production of -galactosidase

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