[10] Screening of peptide libraries linked to lac repressor

Recently developed techniques allow the isolation of peptide ligands for any of a variety of receptor molecules. The most widely used technique for constructing and screening very large peptide libraries involves the display on the surface of filamentous phage. Phage libraries of greater than 1010 different compounds can be screened efficiently, because the phage particle makes a connection between the peptide, fused to a coat protein on the outside of the virion, and the genetic material, encoding that the peptide contained within the virion. This connection allows the isolation of the phage of interest through the binding properties of the peptides, and then the subsequent identification of the peptides through the ability of the genetic material to replicate and yield sequence information. This chapter describes the protocols for the construction and screening of peptides-on-plasmids libraries and for initial characterization of the resulting clones. The protocols that are used here have improved somewhat since the publication of the original paper, describing the technique. The peptides-on-plasmids method is technically more demanding than phage library screening. The procedures described in the original paper and those described here allow efficient enrichment of the receptor-specific peptides.