pBR322 has two restriction sites BamHI (from Bacillus amyloliquefaciens) and SalI (from Streptomyces albus) on the tetracycline-resistant gene (tetR), which acts as a selectable marker. It also has two restriction sites PstI (from Providencia stuartii) and PvuI (from Proteus vulgaris) on the ampicillin-resistant gene (ampR), which also acts as a selectable marker. Hence, these four enzymes can be used. However, the restriction site for PvuII is present on top (replication of plasmid) region. If used, it will interfere with the process of replication of plasmid.