Question

Plasmid used to construct the first recombinant DNA was isolated from which bacterium species?

• A. Escherichia coli
• B. Bacillus thuringiensis
• C. Agrobacterium tumefaciens
• D. Thermus aquaticus

Answer 1

Answer: (A)

Plasmid:

1. Plasmids are small and circular extrachromosomal DNA found in the cells of some organisms like bacteria.
2. Plasmids are widely used as vectors for the production of recombinant DNA.
3. Replication of plasmid is not under the control of chromosomal DNA.
4. Some of the eukaryotes like yeast and plants also contain plasmids.

Plasmid for construction of first rDNA:

1. In 1972, Cohen and Boyer inserted kenamycin (an antibiotic) resistance gene of E. coli in the plasmid pSC101.
2. They then introduced this recombinant plasmid DNA into other strain of E. coli bacteria which did not have resistance against kenamycin.
3. The transformed E.coli bacteria developed kenamycin resistance.
4. The plasmid pSC101 was actually the natural plasmid of bacteria Salmonella typhimurium.
5. Therefore, plasmid used to construct the first recombinant DNA was isolated from Salmonella typhimurium.