Preparation of peptide-targeted phagemid particles using a protein III-modified helper phage

Ligand or peptide-targeted phagemid particles are being pursued as vehicles for receptor-mediated gene delivery. Here we describe a helper phage in which the protein III (pIII) protein is modified by the addition of a ligand peptide sequence at the amino terminus. Phagemid particles can be prepared with the help of this modified helper phage and should display the ligand peptide in most of the pIII proteins on the phagemid surface. Using such a method, it is not necessary for the phagemid to encode the pIII protein, which leaves a larger space for cloning genes of interest. In addition, the technique should allow for the rapid testing of peptide ligands selected from phage display libraries using phagemids encoding various reporter genes (e.g., green fluorescent protein, luciferase, beta-galactosidase) and therapeutic genes.