Plasmid conferring increased sensitivity to mercuric chloride and cobalt chloride found in some laboratory strains of Escherichia coli K-12.

Some lines of the widely used strain CR34 of Escherichia coli K-12 carry a plasmid. The plasmid has a mass of 12 +/- 2 X 10(6) megadaltons and is maintained at a low copy number per cell (1 to 2), and this number is not amplified by growth of cells in the presence of chloramphenicol. The plasmid is designated as pCU3. The presence of pCU3 confers on the strain increased sensitivity to mercuric chloride and cobalt chloride. The plasmid has also been observed to fuse or recombine with the plasmid R64-11.