A cloning vector or cloning vehicle is a DNA molecule in which foreign DNA can be inserted or integrated. This molecule is further capable of replicating within host cell to produce multiple clones of recombinant DNA.
pUC19 and pBR322 (Figure 1) are examples of two forms of plasmids.
Because cloning vectors are self-replicating, they find wide application in gene manipulation.
Characteristics of a Cloning Vector
Origin of replication (Ori)
Ori is a specific sequence of nucleotide in DNA from where replication starts. When foreign DNA is linked to this sequence, then along with vector replication, foreign (desirable) DNA also starts replicating within host cell.
Cloning vector should have restriction sites, to allow cleavage of specific sequence by specific restriction endonuclease.
For example, restriction sites in coli cloning vector pBR322 include HindIII , EcoRI , BamHI , SalI, PvuI, PstI, and ClaI.
Besides ori and restriction sites, a cloning vector must have selectable marker genes.
These genes permit selection of host cells containing recombinant DNA (called transformants) from those, which do not bear them (non-transformants).