Microbiologists are investigating sugar metabolism in wild-type and mutant strains of Escherichia coli. Both strains are found to grow viable colonies on lactose-containing media. Each strain is then cultured on a new growth medium containing only glucose. Representative colonies of each strain from the new media undergo Western blot processing using a fluorescently labeled probe specific for Beta-galactosidase. Wild-type bacterial colonies are found to contain only trace quantities of Beta-galactosidase. However, the mutant colonies express significant amounts of Beta-galactosidase. Further analysis reveals that the variant strain contains a mutation that inhibits the binding of a certain protein to its regulatory sequence. In which of the following locations did this mutation most likely occur?

Question

Microbiologists are investigating sugar metabolism in wild-type and mutant strains of Escherichia coli.  Both strains are found to grow viable colonies on lactose-containing media.  Each strain is then cultured on a new growth medium containing only glucose.  Representative colonies of each strain from the new media undergo Western blot processing using a fluorescently labeled probe specific for Beta-galactosidase.  Wild-type bacterial colonies are found to contain only trace quantities of Beta-galactosidase.  However, the mutant colonies express significant amounts of Beta-galactosidase.  Further analysis reveals that the variant strain contains a mutation that inhibits the binding of a certain protein to its regulatory sequence.  In which of the following locations did this mutation most likely occur?

Quizplus · Accepted Answer

Eductional Objective: The lac operon is regulated by two distinct mechanisms: negatively by binding of the repressor protein to the operator locus and positively by cAMP-CAP binding upstream from the promoter region.  Constitutive expression of the structural genes of the lac operon occurs with mutations that impair the binding of the repressor protein (Lac I) to its regulatory sequence in the operator region.

Microbiologists Are Investigating Sugar Metabolism in Wild-Type and Mutant Strains