Question

In the process of insertional inactivation

• A. a recombinant $DNA$ is inserted within the coding sequence of enzyme $\beta$-galactosidase, resulting in inactivation of the enzyme
• B. a recombinant $DNA$ is inserted within the coding sequence of proteins involved in the replication of the plasmid
• C. a recombinant $DNA$ is inserted within the recognition site for EcoRI
• D. none of the above

Answer 1

Answer: (A)

Alternative selectable markers have been developed which differentiate recombinants from the non-recombinants on the basis of their ability to produce colour in the presence of a chromogenic substrate. In this, a recombinant $DNA$ is inserted within the coding sequence of an enzyme, $p$-galactosidase. This results into inactivation of the enzyme, which is referred to as insertional inactivation. The presence of a chromogenic substrate gives blue coloured colonies if the plasmid in the bacteria does not have an insert. Presence of insert results into insertional inactivation of the $P$-galactosidase and the colonies do not produce any colour, these are identified as recombinant colonies.