A novel nabelschnur protein regulates segregation of the kinetoplast DNA in Trypanosoma brucei.

The acquisition of mitochondria was imperative for initiating eukaryogenesis and thus is a characteristic feature of eukaryotic cells. The parasitic protist Trypanosoma brucei contains a singular mitochondrion with a unique mitochondrial genome, termed the kinetoplast DNA (kDNA). Replication of the kDNA occurs during the G phase of the cell cycle, prior to the start of nuclear DNA replication. Although numerous proteins have been functionally characterized and identified as vital components of kDNA replication and division, the molecular mechanisms governing this highly precise process remain largely unknown. One division-related and morphologically characteristic structure that remains most enigmatic is the "nabelschnur," an undefined, filament-resembling structure observed by electron microscopy between segregating daughter kDNA networks. To date, only one protein, TbLAP1, an M17 family leucyl aminopeptidase metalloprotease, is known to localize to the nabelschnur. While screening proteins from the T. brucei MitoTag project, we identified a previously uncharacterized protein with an mNeonGreen signal localizing to the kDNA as well as forming a point of connection between dividing kDNAs. Here, we demonstrate that this kDNA-associated protein, named TbNAB70, indeed localizes to the nabelschnur and plays an essential role in the segregation of newly replicated kDNAs and subsequent cytokinesis in T. brucei.