PRODUCTION OF PROTEINS, PLASMIDS CODING THEREFOR AND ORGANISMS CONTAINING SUCH PLASMIDS

Plasmids which comprise: (1) an origin of replication; (2) an additional sequence required for plasmid replication or preferably a gene giving a selective advantage; and (3) two expression cassettes each of which are located between (1) and (2) but are separated by (1) and (2) from each other; and which are free from inverted repeat sequences (other than in (3)) are highly persistent though successive generations of microbes containing them.