Q.pBR 322, BR stands for :

A vector (cloning vehicle) is a small, self-replicating DNA molecule used to carry and transport a DNA fragment into a host cell for propagation, splitting functionally into cloning vectors (which simply propagate an insert) and expression vectors (which additionally carry the signals needed to translate the insert into protein, e.g. pUC19). A workable vector must be small (under about 10 Kb), carry an origin of replication (ori), a selectable marker (typically antibiotic resistance) and a Multiple Cloning Site (MCS/polylinker) of unique restriction sites. The major named vector families are: plasmids (extrachromosomal, self-replicating circular bacterial DNA - pBR322, built by Bolivar and Rodriguez, being the classic 4361 bp example, and the tumour-inducing Ti plasmid of Agrobacterium tumefaciens being the key plant-biotechnology example); transposons ('jumping genes' that insert without sequence relationship to their target site); cosmids ( …