Direct Selection of cDNAs by Phage Display

Dozens of genomes will be partly or completely sequenced over the next few years. In the post genomic area, we are now facing the challenge of functionally characterizing thousands of genes generated by the genome projects. Selective enrichment of clones encoding a desired gene product and rapid handling of large numbers of individual clones resulting from screening of molecular libraries bear the potential to facilitate progress in this field. Phage surface display technology, first described by Smith (11 ), enables the construction of large combinatorial peptide and antibody libraries. The basic concept of phage display links the phenotype, expressed as fusion together with a phage surface coat protein, to its genetic information integrated into the phage genome. This procedure allows to survey large libraries for the presence of specific clones using the discriminative power of affinity selection (2 –4 ). The selection of cognate phage (biopanning) is achieved by interaction between a solid phase-coated ligand and the phage library applied in fluid phase during multiple rounds of phage growth and selection. The field of phage display technology has developed rapidly, and antibodies, enzymes, enzyme inhibitors, hormones, DNA binding molecules, and allergens have been successfully selected from molecular libraries (5 –11 ). These examples clearly demonstrate the general applicability of linking genotype and phenotype to phage coat proteins. Molecular libraries allow the rapid identification of peptide-ligand interactions. In combination with high-throughput screening technology, they will play an important role in a rational approach for the identification of gene products (12 ,13 ).