pBR322 is a plasmid and one of the most commonly used E. coli cloning vectors. pBR322 was the first artificial plasmid created by Mexicans Bolivar and Rodriguez and was named eponymously after the scientist duo. pBR322 is 4361 base pairs in length and contains a replicon region (source plasmid pMB1) and the tet gene, encoding the tetracyclinetance protein (source plasmid pSC101). It also contains the unique EcoRI restriction site GAATTC and splices the DNA between G and A from 5' to 3' position. The origin of replication in this plasmid is pMB1 (a close relative of ColE1).