A tubulin-like, filament forming GTPase; the motor component of the type III plasmid partition system which ensures correct segregation of the pBtoxis plasmid. Filaments may seed from the centromere-like site (tubC) when bound by DNA-binding protein TubR; the tubC-TubR complex stabilizes the TubZ filament. Filaments grow at the plus end and depolymerize at the minus end, a process called treadmilling. TubR-tubC complexes track the depolymerizing minus end of the filament, probably pulling plasmid within the cell (PubMed:20534443, PubMed:23010931, PubMed:25825718). Required for pBtoxis plasmid replication/partition (PubMed:16936050, PubMed:17873046). Binds the TubR-tubC complex; GTP is not required for binding to TubR-tubC. TubZ alone does not bind DNA (PubMed:17873046, PubMed:20534443, PubMed:25825718). Has a high GTPase activity in the presence of Mg(2+); in the presence of GTP assembles into dynamic filaments which upon polymerization bind almost exclusively GDP. Filament formation is cooperative, requiring a critical concentration. Formation occurs very quickly and is followed by disassembly as GTP is consumed (PubMed:18198178). GTP + H2O = GDP + H(+) + phosphate In the GTP-gamma-S-bound filament structure all subunits bind Mg(2+), in the GDP-bound filament less than half the subunits bind Mg(2+). GTPase is inhibited by GTP-gamma-S, which also stabilizes filaments. Forms filaments; a 2-stranded filament forms with the non-hydrolyzable GTP-gamma-S which is probably a precursor to the 4-stranded filament that forms in the presence of GTP. The 4-stranded form binds GDP (PubMed:18198178, PubMed:20974911, PubMed:24550513). In vivo polymerizes to form dynamic filaments that often extend from one cell pole to the other, moving in a unidirectional manner. Filaments polymerize at the plus end and depolymerize at the minus end, a process called treadmilling. Polymerization only occurs above a critical concentration, it does not require upstream tubR (PubMed:17510284, PubMed:25825718). The tubC DNA-TubR complex binds to TubZ (PubMed:17873046, PubMed:20534443). Forms long, dynamic filaments. Probably part of the tubR-tubZ operon. Consists of two domains: a nucleotide-binding N-terminus that hydrolyzes GTP and a C-terminus domain necessary for polymerization. The domains are bridged by a long, central helix (PubMed:20534443, PubMed:20974911, PubMed:24550513). The C-terminus is required for binding to the TubR-iteron DNA complex; its gradual deletion leads to decreasing binding to TubR-DNA (PubMed:20534443). Interactions between the C-terminus and the following monomer drive polymerization (By similarity). The C-terminus is required for filament formation (PubMed:24550513). In the absence of GTP's gamma phosphate the intersubunit interface is weakened, linking GTP hydrolysis to treadmilling (PubMed:20974911). Loss of plasmid replication. A miniplasmid containing this and upstream gene tubR is able to replicate in B.thuringiensis subsp. israelensis and express insect toxin proteins. The miniplasmid could be used to make plasmids for insect toxin overexpression. N-terminally tagged protein does not form filaments, C-terminally tagged protein does so, but not as well as untagged protein. The pBtoxis plasmid encodes all the major endotoxin proteins (Cyt1Aa, Cry4Aa, Cry4Ba, and Cry11Aa) responsible for the mosquito larvicidal activity of strain 4Q2. Belongs to the FtsZ family. TubZ subfamily.