Exogenous factors that induce the expression of such RNA polymerase or an increase in the copy number of the plasmid vector include, but are not limited to, for example, the addition of various chemicals, such as lactose or structurally related substances like isopropyl-??-D-thiogalactoside (IPTG), galactose or structurally related substances, and arabinose or structurally related substances; the