3.3.3 Vectors

The fragments produced by the action of the restriction enzymes, which represent a specific gene, have to be moved and introduced into a recipient cell.  Vehicles known as vectors can achieve this. These vectors could be either plasmids, which are naturally occurring in bacteria or different types of viruses.  The plasmid is a double–stranded DNA molecule that can replicate autonomously within the bacterial cells. They are present as a separate small circular molecule, and contain a number of restriction sites and specific antibiotic resistance genes. The presence of this resistant gene can help in detecting the success of recombinant DNA formation.

Other types of vectors are the viruses. The bacteriophage Lambda is widely used in recombinant DNA. Other types of viruses can also be used as a vector especially for gene therapy such as retroviruses, adenoviruses and adenoassociated viruses. When the fragments produced by the action of restriction enzymes are put together with a vector after treating both the fragments and vectors with the same restriction enzyme. The two types of DNA are joined together using ligase enzymes i.e. the vector and the DNA fragment forming the recombinant DNA.