A low-copy expression vector has been constructed from a 9 Kbp region of the Escherichia coli F plasmid containing the oriV and oriS origins of replication. This plasmid carries the beta-lactamase gene (Apr) and the araBAD promoter/araC regulator for arabinose-inducible gene expression. A derivative which carries a lacZ reporter gene was found to be stably maintained for at least 150 generations. A related multi-copy plasmid was stably maintained in arabinose-free medium, but no plasmid-bearing segregants remained after 60 generations when lacZ expression was induced. Induced expression resulted in 27% (multi-copy) and 12% (low-copy) decreases in growth rate. The uninduced levels of beta-galactosidase were 200 units (multi-copy) and 15 units (low-copy).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.