Identify the enzyme in which recombinant DNA is inserted within the coding sequence for cloning.
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → β-galactosidase
A cloning vector needs a way to show which bacteria took up the foreign gene. In the insertional inactivation method, the foreign DNA is inserted inside the coding sequence of the gene for an enzyme. The enzyme is then no longer made. With a colour-giving (chromogenic) substrate, bacteria that hold an empty vector turn blue. Bacteria that hold the insert stay colourless, so the recombinant colonies are easy to pick out.
(1) Cellulase — Incorrect. It breaks the cellulose wall of plant cells. It is used to release DNA and is not a marker.
(2) Permease — Incorrect. It is another protein of the lac operon, which carries lactose into the cell. It is not the enzyme used for this screening.
(3) Transacetylase — Incorrect. It is the third protein of the lac operon, and it too is not used for screening.
(4) β-galactosidase — Correct. The recombinant DNA is inserted within its coding sequence, so the enzyme is inactivated and no blue colour forms.
NCERT Extract:
Cloning Vectors – …
