Nuclear localization signals in phage terminal proteins provide a novel gene delivery tool in mammalian cells

Terminal proteins (TPs) of bacteriophages prime DNA replication and become covalently linked to the genome ends. Unexpectedly, we have found functional eukaryotic nuclear localization signals (NLSs) within the TP sequences of bacteriophages from diverse families and hosts. Given the role of bacteriophages as vehicles for horizontal gene transfer (HGT), we postulated that viral genomes that have covalently linked NLS-containing terminal proteins might behave as vectors for HGT between bacteria and the eukaryotic nucleus. To validate this hypothesis, we profited from the in vitro Φ29 amplification system that allows the amplification of heterologous DNAs producing linear molecules of DNA with TP covalently attached to both 5' ends. Interestingly, these in vitro-generated TP-DNA molecules showed enhanced gene delivery in mammalian cells, supporting a possible role in HGT by transferring genes between prokaryotes and eukaryotes. Moreover, these TP-DNA molecules are a useful tool to amplify and subsequently deliver genes efficiently into the eukaryotic nucleus. Here, we suggest various possible applications and further developments of the technique with biotechnological and therapeutic purposes.