Abstract: A plasmid having an insertion site for a eukaryotic DNA fragment adjacent to a bacterial promoter and downstream from a prokaryotic ribosome binding site and initiator codon such that the bacterial promoter controls transcription and translation of an inserted DNA fragment is disclosed.The production and use of such plasmids is also disclosed.In general terms, one aspect of the present invention relates to a series of plasmid vectors having the basic characteristic of a Hind III insertion site adjacent to a tryptophan promoter and also a gene for tetracycline resistance. The plasmid vectors are by virtue of the structure thereof ideally suited to receive at the Hind III site an inserted eukaryotic DNA fragment the transcription and translation of which is under the control of the tryptophan promotor.