Direct selection of cDNAs from filamentous phage surface display libraries: potential and limitations

Over the past decade, powerful technologies devoted to survey large molecular libraries for the presence of specific clones using the discriminative power of affinity selection have been developed. Phage surface display technology is the most established of these methods and has revolutionised our ability to select agonistic and antagonistic peptides, antibodies with desired specificity and other drug targets. Thereby ligands are expressed as fusions to phage coat proteins and their respective genes are packaged within the phage. The basic concept of linking the phenotype, expressed as gene product displayed on the phage coat, to its genetic information integrated into the phage genome, creates fusion proteins covalently associated with the infectious particle itself. Binding of the phage to the target molecule offers a selective system by which rare phage carrying the desired gene product can be selected from large phage populations carrying inappropriate sequences. Phage selected in this fashion can be used for subsequent rounds of selection because they are able to self-replicate in suitable host cells, yielding target-specific phage populations after several consecutive rounds of affinity selection. Over 1500 publications describe the use of phage display technology highlighting its performance. Phage display possesses certain limitations, including its use for selection of genes from cDNA libraries that has lagged behind, despite the many accomplishments of this technology. Here we discuss recent progress in construction and screening of cDNA libraries displayed on phage surface and emerging concepts allowing fast identification of virtually all different clones present in enriched libraries.