Overproduction of EcoRI and SpA::EcoRI fusion protein by Escherichia coli employing the combinations of three different types of multicopy plasmids: Comparison of plasmid stabilities and product concentrations

The copy numbers of the expression plasmids (pRTF309+ and pMTC48), the repression plasmids (pcI857 and pRK248cI) and the protection plasmid (pEcoR4) in recombinant E. coli JM103 were investigated. In the absence of the protection plasmid, the copy number of the expression plasmid dropped; in its presence, the copy numbers of the expression plasmids increased after gene expression by temperature-shift induction. The copy numbers of the repression plasmids were not influenced by the presence or absence of the protection plasmid. The copy number of the latter were not changed during temperature-induced gene expression. In the absence of the protection plasmid, the product concentration (EcoRI enzyme activity) was very low. With the plasmid combination pRTF309+, pRK248cI, and pEcoR4, the enzyme (EcoRI) activity was higher, but with the plasmid combination pMTC48, pRK248cI, pEcoR4, the enzyme (SpA::EcoRI) activity was highest.