The successful linkage of the antibiotic resistance gene with the plasmid vector was facilitated by which enzyme?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → DNA ligase
Recombinant DNA is made in two steps: cutting and joining. Restriction enzymes cut the DNA at specific places. Another enzyme must then join the cut piece to the vector.
Option (1) DNA ligase — Correct. DNA ligase joins the ends of cut DNA molecules. It sealed the antibiotic resistance gene into the plasmid and so made the first recombinant DNA, a circular DNA that could copy itself.
Option (2) RNA ligase — Incorrect. RNA ligase joins pieces of RNA. Both the gene and the plasmid are DNA, so an RNA-joining enzyme could not link them. It is not one of the tools of recombinant DNA technology.
Option (3) DNA polymerase — Incorrect. DNA polymerase builds new DNA strands by copying a template, as in replication and PCR. After the plasmid entered E. coli, the host’s DNA polymerase made copies of it, but this enzyme does not join two cut pieces.
Option (4) RNA polymerase — Incorrect. RNA polymerase makes RNA from a DNA template during transcription. It plays no part in joining a gene to a plasmid.
NCERT Extract:
Principles of Biotechnology – “… Stanley Cohen and Herbert Boyer accomplished this in 1972 by isolating the antibiotic resistance gene by cutting out a piece of DNA from a plasmid which was responsible for conferring antibiotic resistance. The cutting of DNA at specific locations became possible with the discovery of the so-called ‘molecular scissors’– restriction enzymes. The cut piece of DNA was then linked with the plasmid DNA. … The linking of antibiotic resistance gene with the plasmid vector became possible with the enzyme DNA ligase, which acts on cut DNA molecules and joins their ends.”