Discussion

The mitochondrial genome encodes essential proteins involved in oxidative phosphorylation and thus, the genes for these proteins must be faithfully inherited during cell division. However, only little is known about the molecular mechanisms of mitochondrial genome inheritance. Here, we have discovered an outer mitochondrial membrane (OM) protein complex, which is crucial for mitochondrial genome inheritance in the parasitic protozoan Trypanosoma brucei. The tripartite attachment complex (TAC) functions as the mitochondrial genome segregation machinery in trypanosomes, which spans both mitochondrial membranes and physically links the basal body of the flagellum to the single-unit mitochondrial genome. TAC40 is a β-barrel membrane protein and reciprocal pulldown experiments demonstrate that it occurs in a distinct and stable complex with two novel TAC components, namely TAC60 and TAC42. By immunofluorescence analysis (IFA) we show that TAC60 depends on its N-terminus for proper TAC localization. Moreover, we demonstrate that the kinetoplastid-specific TAC60 and TAC42 proteins are both OM proteins and intriguingly, that TAC42 represents an additional β-barrel membrane protein in the TAC. Thus, the mitochondrial genome segregation machinery in trypanosomes includes a specialized OM protein complex, which is composed of three proteins, including two distinct β-barrel proteins.