It is a plasmid and was one of the first widely used E. coli cloning vectors.
It is a circular double-stranded molecule 4,361 base pairs in length and contains the genes for resistance to ampicillin and tetracycline and can be amplified with chloramphenicol.
Role of ORI:
Ori is the origin of replication in pBR322, where replication starts.
Ori is a genetic sequence that acts as the initiation site for the replication of DNA.
Any fragment of DNA, when linked to the ori region, can be initiated to replicate.