DNA segregation is a fundamental process that needs to be performed with high precision in order to ensure stable genome transmission during the cell cycle. In prokaryotes, plasmids have been used as tractable model systems to understand the minimal molecular requirements and the underlying mechanism during DNA segregation. Most of low-copy number plasmids use the so-called partition systems for their maintenance, which are compact genetic modules tightly auto-regulated by one or both of the gene products. These systems require only three elements: a centromere-like site, a centromere-binding protein (CBP), and a motor NTPase protein. The CBP binds to the centromere-like site forming a nucleoprotein complex known as segrosome, which is recognized by the motor protein that effectively moves the DNA within the cell. According to the nature of the motor protein, partition systems have been classified into: Type I (Walker-A ATPase), Type II (actin-like ATPase) and Type III (tubulin-like GTPase).
Type III partition systems have been identified as part of the maintenance machinery of virulence plasmids in Bacillus and Clostridium species, where the CBP is a small protein (~10KDa) named TubR that binds to centromere-like site tubC and, the motor protein, TubZ, is a prokaryotic tubulin homologue that assembles into helical cytomotive filaments.
Unraveling the macromolecular arrangement of CBP proteins and centromere-like sites is key to understand the maintenance of virulence factors in bacteria.
Topic-related papers of the group
Martín-García B.*, Martín-González A.*, et al. Nucleic Acids Research 14 May; gky370, https://doi.org/10.1093/nar/gky370 (2018). The TubR-centromere complex adopts a double-ring segrosome structure in Type III partition systems.LINK
Fuentes-Pérez ME et al. Scientific Reports Feb 23; 7:43342. doi: 10.1038/srep43342 (2017). TubZ filament assembly dynamics requires the flexible C-terminal tail. LINK
