Vectors are essentially carrier DNA molecules in
possession of the following properties:
They must be able to replicate independently.
They should contain a number of restriction enzyme cleavage sites. These are the sites where
restriction enzymes will cut and the foreign DNA inserted.
They should carry selectable markers (in the
form of antibiotic resistance gene) to distinguish host
cells that carry the vectors and host cells that do not
contain the vectors.
Plasmids are the most often used vectors.
They are small, circular, dispensable genetic elements that are
found in most bacteria cells. They can be beneficial to host
cell, since it can provide drug or heavy metal resistance or
produce some toxic protein.
pBR322 is the most
commonly used plasmid. It has 2 selectable marker genes (one
conferring resistance to antibiotic tetracycline and the other
confers resistance to antibiotic ampicillin) and a number of
unique sites for restriction enzymes to cut.