Question

A researcher engineers a lac operon on a plasmid inactivating all parts of the lac operator and the lac promoter, replacing them with the binding site for the LexA repressor and promoter regulated by LexA. The plasmid is introduced into E.coli cells that have a lac operon with an inactive lacZ gene. Under what conditions will these transformed cells produce β-galactosidase?

• A. On subjecting E.coli cells to high levels of a DNA-damaging agent like UV light
• B. On starving E.coli cells
• C. On growing E.coli cells in lactose-rich medium
• D. On co-culturing E.coli cells with B subtilis

Hint:

LexA regulates the SOS response in bacteria, which is activated during DNA damage.

Answer 1

The Correct Option is A

The LexA protein represses genes in the SOS response pathway. Under DNA damage (e.g.,UV light), LexA is cleaved, allowing transcription of genes it regulates. This engineering enables the production of β-galactosidase in response to LexA degradation caused by DNA damage.