A probable TubZ filament regulator that is part of the type III partition system presumably used to ensure correct segregation of this bacteriophage. Binds to TubZ in the presence of GTP and Mg(2+), and to TubZ-TubR-tubC (tubC is the centromere-like site). The latter complex is reshaped from large bundles to rings by TubY (PubMed:22538818). Modifies TubZ filaments formed in the presence of GDP to make them thinner and more flexible; in GDP and lacking the last 8 residues of TubZ makes rings without TubT-tubC (PubMed:28230082). Forms homooctamers in the absence of the last 13 residues; the coiled coil domain is required for oligomerization. In the presence of GTP and Mg(2+) binds to TubZ and also to TubZ-TubR-tubC DNA; the latter is reshaped from large filament bundles to rings of 30-40 nm diameter. The coiled coil domain is required for oligomerization and for binding to TubZ, but the C-terminal 13 residues are not. This bacteriophage also exists as a circular plasmid prophage in its host.