Phage-Based Expression Systems

Abstract

Abstract Phage, and plasmid, derivatives that had ‘‘picked up’’ genes from the Escherichia coli chromosome led Campbell (12) to propose his influential model based on recombination between circular genomes (see chapter 7). According to this model, segments of bacterial DNA were added to a phage genome if excision of the prophage was by an ‘‘aberrant’’ recombination event. These unexpected, or illegitimate (2, 27, 96) events fortuitously created the early recombinant clones that became tools at the cutting edge of research in the pioneering days of molecular biology. They, for example, facilitated the analyses of bacterial operons (30, 61) and enabled the amplification of the Lac repressor (60). Monitoring the bacterial enzymes specified by ltrp phages enhanced our understanding of the regulatory mechanisms of bacteriophage λ (18, 28, 29), telling us much about the control of transcription from the early λ promoters and suggesting how a phage promoter might be harnessed to amplify gene products. While these first ‘‘recombinant clones’’ of phages and plasmids were of unpredictable content, by 1974 it was possible to design and make new combinations of genes from any source in either plasmid (15) or phage λ vectors (62, 76, 92). This article will introduce the use of λ promoters within the context of the phage genome and follow the use of these and other phage promoters as components of genetically engineered plasmids, where they are relieved of their essential roles in the normal life cycle of the phage and instead used to amplify gene products.