Question

Explain how the lethal gene in the plasmid's multiple cloning site(MCS) will function with and without a DNA insert.

Answer 1

lethal gene is present in the multiple cloning site,

a) if there is no DNA insert

there is no DNA insert in the MCS, so the lethal gene is intact, it is transcribed and translated to produce the protein product, which causes the death of the cell, so those cells which have taken the plasmid without the insert dies.

b) with a DNA insert

MCS is digested using the restriction enzymes and the DNA is inserted into the MCS, the inserted DNA disrupts the lethal gene, so functional RNA or protein is not produced from the lethal gene, so it cannot cause the death of the cells so those cells which have taken the plasmid with the DNA insert are viable.

so lethal gene in the MCS helps us to select those cells which have taken the plasmid with the insert.