You are using a gene fusion between a virulence gene (vir) and lacZ to study the regulation of vir by acidic pH. (When lacZ is expressed, cells are blue; when lacZ is not expressed, cells are white.)...

You are using a gene fusion between a virulence gene (vir) and lacZ to study the regulation of vir by acidic pH. (When lacZ is expressed, cells are blue; when lacZ is not expressed, cells are white.) You introduce a transposon into the strain with the vir-lacZ fusion and screen for regulatory mutants. You conclude that vir is not expressed at an acidic pH because you observe that, for the wild-type fusions, colonies are on an acidic medium (pH 5.0) and on a neutral medium (pH 7.0). In a mutant strain, you conclude that the transposon has inserted into a gene encoding a repressor protein because you observe that colonies are on the acidic medium and on the neutral medium.

A. blue ... white ... blue ... blue

B. white ... blue ... blue ... blue

C. blue ... white ... white ... white

D. white ... blue ... white ... white

E. white ... blue ... white ... blue