Expression vector permitting complete repression of transcription before induction. Useful for cloning products that may be toxic to the host. [3] Deposited by: J.G.Campbell Grwoth media: LB plus ampicillin (ATCC medium number 1227) 37C Hosts: E.coli. Related vectors: pBR322, pT7-0, pT7-1, pT7-2, pT7-7, pT7-SCII.