Plasmid pUC18

    A plasmid is a circular dsDNA molecule a few hundred or thousand base pairs in circumference. Naturally-occuring plasmids are viruses of bacteria. The artificial plasmid pUC18 has been genetically engineered to include a gene for antibiotic resistance to Ampicillin (ampR), and a  gene (and its promoter) for the enzyme beta-galactosidase (lacZ). The lacZ gene contains a polylinker region, with a series of unique restriction sites found nowhere else in the plasmid. Digestion with any one of these endonucleases will make a single cut that linearizes the circular plasmid DNA, and allow it to recombine with foreign DNA that has been cut with the same endonuclease.

Figures © 2002 by Griffiths et al.; all text material © 2011 by Steven M. Carr