CONSTRUCTION AND SCREENING OF M13 PHAGE LIBRARIES DISPLAYING LONG RANDOM PEPTIDES

We have constructed two phage display libraries expressing N-terminal pIII fusions in M13 composed of 37 and 43 random amino acid domains, r espectively. The D38 library expresses 37 random amino acids with a ce ntral alanine residue, and the DC43 library contains 43 random amino a cids with a central cysteine flanked by two glycine residues, giving t he displayed peptide the potential to form disulfide loops of various sizes. We demonstrate that the majority of random sequences in both li braries are compatible in pentavalent display with phage viability. Th e M13 phage display vector itself has been engineered to contain a fac tor Xa protease cleavage site to provide an alternative to acid elutio n during affinity selection. An in-frame amber mutation has been inser ted between the pIII cloning sites to allow for efficient selection ag ainst nonrecombinant phage in the library. These libraries have been p anned against mAb 7E11-C5, which recognizes the prostate-specific memb rane antigen (PSM). Isolated phage display a consensus sequence that i s homologous to a region in the PSM molecule.