Plasmids are the most commonly used vectors. The position of functional DNA sequences, which includes origin of replication (ORI), antibiotic resistance (AmpR), promoter, and terminator, on a plasmid are depicted in vector maps.

Figure 1: Example of a vector map.

To proliferate a plasmid inside a host cell it needs to contain an origin of replication (ORI) that is specific to the host cell.