Lambda phage promoter used to enhance expression of a plasmid-cloned gene

A 50-fold (or greater) increase in the production of phage 21 repressor was obtained by construction of a plasmid in which the 21cI (repressor) gene could be transcribed from lambdaPL. The enhancement due to increased 21cI gene copy number and transcription from lambdaPL were at least five-fold and ten-fold, respectively. The plasmid was constructed in vitro by recombination of EcoRI-generated DNA fragments. The use of the DNA fragment containing lambdaPL in obtaining expression of cloned genes is discussed.