Interactions between viruses and their host's cytoskeletal proteins have proven to be essential components of viral infections. Newly sequenced bacteriophages have genes encoding their own putative cytoskeletal proteins, but nothing was known about what role these viral cytoskeletal proteins might play in infection. Here I characterize the first bacteriophage tubulin homolog, PhuZ, and demonstrate that it has an important and conserved role during lytic growth. It is the first prokaryotic tubulin shown to be dynamically unstable in vivo and actively position a mass of phage DNA in the center of the infected cell. This positioning is important for encapsidation of phage DNA and subsequent production of progeny phage. PhuZ polymerizes by a unique mechanism that requires its extended C-terminal tail and potentially forms a three- stranded filament, a reduced prokaryotic version of the eukaryotic microtubule. Using mass spectrometry, we have determined that PhuZ is among the proteins encoded in the phage genome that are only expressed inside the infected cell and are not found in the mature virio
