The presence of a non-mutant lacI gene and a mutated lacOc sequence would result in constitutive expression of the lacZ gene and fluorescence of the cells, both in the presence and absence of inducer.
In the genetically engineered fluorescent strain, if the lacI gene remained non-mutant but the lacO sequence on the chromosome mutated to lacOc, the cells would fluoresce in the presence of inducer but not in the absence of inducer.
This is because the lacI gene encodes the LacI repressor protein, which binds to the lacO operator sequence and prevents transcription of the lacZ gene.
The lacZ gene encodes the β-galactosidase enzyme, which catalyzes the conversion of lactose into galactose and glucose. When lactose is present, it acts as an inducer and binds to LacI, causing it to change shape and release the lacO operator.
This allows transcription of the lacZ gene, resulting in the production of β-galactosidase. β-galactosidase can then cleave a substrate called X-gal, producing a fluorescent blue product.
The lacOc mutation alters the structure of the lacO operator sequence, preventing LacI from binding to it effectively.
Question
If the lacI gene in the genetically engineered fluorescent strain were nonmutant but the lacO sequence on the chromosome mutated to lacOc, how would the cells fluoresce in the presence of inducer? In the absence of inducer?