Bacteriophage lambda-E. coli K12 vector-host system for gene cloning and expression under lactose promoter control: I. DNA fragment insertion at the lacZ EcoRI restriction site.

Summary Bacteriophage lambda vectors, derived from plac5 were constructed. Their genomes have only one EcoRI restriction site, located near the end of the -galactosidase gene. Recombinants, constructed in vitro, having a DNA fragment inserted in the EcoRI site, are lac^- and can be easily recognized. Expression of such foreign genes is then under the control of the lac promoter. Mutations Qam73 and Sam7 greatly increase the amount of -galactosidase synthesized by the vector bacteriophage. The ZEQS vector has been certified B2 (EK2) by the French control commission Recombinaisons génétiques in vitro.