PLASMIDS WITH CONDITIONAL UNCONTROLLED REPLICATION BEHAVIOUR

摘要

Plasmids useful as cloning vectors which carry a regulatable promoter which has been inserted in such a way that transcription from the promoter regulates replication so that increased transcription leads to a substantially increased or uncontrolled plasmid copy number when host microorganisms containing the plasmid are cultivated under conditions securing such increased transcription. The regulatable promoter is preferably lambda PR, the activity of which is controlled by a temperature-sensitive lambda cl repressor. To obtain gene products of the plasmids, host microorganisms to which such plasmids have been transformed are cultivated at about 30C to secure a constant, low plasmid copy number during the seeding and multiplication stages of the microorganism, after which the temperature is shifted to about 36-42C to obtain an uncontrolled plasmid copy number and an amplified amount of gene product. The gene product is then harvested from the culture.