If a nonsense mutation is present in the LacZ gene of the lac operon, the mRNA of \beta -galactosidase would
If a nonsense mutation is present in the LacZ gene of the lac operon, the mRNA of-galactosidase would
Select an option to attempt
Correct Answer: Option B
Explanation
The lac operon regulation in E. coli: The lac repressor (LacI protein) is constitutively expressed. In the ABSENCE of lactose: repressor binds operator (O1, O2, O3) → RNA Pol cannot transcribe. In the PRESENCE of lactose: allolactose (metabolite of lactose) binds repressor → conformational change → repressor releases operator → RNA Pol transcribes lacZYA. A NONSENSE MUTATION in lacZ creates a premature stop codon within the lacZ ORF. This does NOT affect: (1) The lac promoter or operator; (2) The lac repressor gene (lacI); (3) The ability of the operon to be induced by lactose/allolactose. Therefore, the lacZYA mRNA IS transcribed in response to lactose (the promoter/operator is fully functional) but produces a truncated, non-functional-galactosidase. The mRNA is made but the protein is non-functional.