PBR322

pBR322 is a plasmid and for a time was one of the most commonly used E. coli cloning vector. Created in 1977, it was named eponymously after its Mexican creators, p standing for plasmid, and BR for Bolivar and Rodriguez.

pBR322 is 4361 base pairs in length and contains a replicon region (source plasmid pMB1), the amp^R gene, encoding the ampicillin resistance protein (source plasmid RSF2124) and the tet^R gene, encoding the tetracycline resistance protein (source plasmid pSC101). The plasmid has unique restriction sites for more than forty restriction enzymes. 11 of these 40 sites lie within the tet^R gene. There are 2 sites for restriction enzymes HindIII and ClaI within the promoter of the tet^R gene. There are 6 key restriction sites inside the amp^R gene. The origin of replication or ori site in this plasmid is pMB1 (a close relative of ColE1). The ori encodes two RNAs (RNAI and RNAII) and one protein (called Rom or Rop).

The circular sequence is numbered such that 0 is the middle of the unique EcoRI site and the count increases through the tet genes. The ampicillin resistance gene is a penicillin beta-lactamase. Promoters P1 and P3 are for the beta-lactamase gene. P3 is the natural promoter, and P1 is artificially created by the ligation of two different DNA fragments to create pBR322. P2 is in the same region as P1,...
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