A Bipartite Bacteriophage T4 SOC and HOC Randomized Peptide Display Library: Detection and Analysis of Phage T4 Terminase (gp17) and Late σ Factor (gp55) Interaction

HOC and SOC are dispensable T4 capsid proteins that can be used for phage display of multiple copies of peptides and proteins. A bipartite phage T4 peptide library was created by displaying on tetra-alanine linker peptides five randomized amino acids from the carboxyl-terminus of SOC and five randomized amino acids from the amino terminus of HOC. The bipartite library was biopanned against the phage T4 terminase large subunit gp17 to identify T4 gene products that may interact with the terminase. The sequences of selected phages displayed matches to those T4 gene products previously known by genetic and biochemical criteria to interact with gp17: gp20 (portal protein), gp32 (single-stranded DNA binding protein), gp16 (terminase small subunit), and gp17 (self). In addition, matches were found to gp55 (T4 late σ factor), gp45 (sliding clamp), gp44 (clamp loader), gp2 (DNA end protein), and gp23 (major capsid protein).