pUC19

pUC19 is a small, high-copy plasmid cloning vector used in molecular biology for Escherichia coli. It is part of the pUC plasmid series, designed to maximize yield of recombinant plasmids and simplify screening and sequencing. The backbone originates from pMB1 with an origin of replication that promotes a very high copy number in standard E. coli strains.

Key features of pUC19 include a 2686-base pair circular DNA molecule, an ampicillin resistance gene (AmpR) for selection, and a multiple cloning site (MCS) located within the lacZ alpha fragment of the beta-galactosidase gene. The MCS contains multiple unique restriction enzyme sites, enabling convenient insertion of foreign DNA. The vector also contains flanking M13 priming sites to facilitate sequencing of inserts. In blue/white screening, insertion into the lacZ alpha region disrupts alpha-complementation, yielding white colonies on media containing X-gal and IPTG, while non-recombinant colonies appear blue.

Because of its high copy number and simple antibiotic selection, pUC19 is widely used for cloning small DNA fragments, plasmid amplification, and routine plasmid preparation. It is typically propagated in standard laboratory strains of E. coli. Limitations include potential instability with certain inserts due to high copy number and the possibility that very large inserts or toxic sequences may be problematic in this backbone.

History and impact: pUC19 and the pUC series became standard tools in cloning workflows during the 1980s and 1990s, valued for blue/white screening, convenient sequencing, and reliable propagation of recombinant DNA.