ColD-derived cloning vectors that autoamplify in the stationary phase of bacterial growth.

The construction of cloning vectors based on the replicon of plasmid ColD-CA23 is reported. These vectors, like ColD itself, autoamplify when cultures of host bacteria enter the stationary phase of growth, thereby resulting in a substantial increase in the expression of cloned genes as a consequence of the increase in gene dosage. The principal advantage of these vectors is that, unlike the situation pertaining to other expression vectors, the increase in expression of genes cloned in ColD vectors does not require any experimental intervention (i.e., occurs naturally), and takes place at high cell densities. The vectors show high stability in Escherichia coli strains and are compatible with ColE1-type cloning vectors.