The assembly of F1FO-ATP synthase is disrupted upon interference of RNA editing in Trypanosoma brucei

Throughout eukaryotes, the gene encoding subunit 6 (ATP6) of the F1FO-ATP synthase (complex V) is maintained in mitochondrial (mt) genomes, presumably because of its high hydrophobicity due to its incorporation into the membrane-bound FO moiety. In Trypanosoma species, a mt transcript that undergoes extensive processing by RNA editing has a very low sequence similarity to ATP6 from other organisms. The notion that the putative ATP6 subunit is assembled into the FO sub-complex is ostensibly challenged by the existence of naturally occurring dyskinetoplastic (Dk) and akinetoplastid (Ak) trypanosomes, which are viable despite lacking the mtDNA required for its expression. Taking advantage of the different phenotypes between RNA interference knock-down cell lines in which the expression of proteins involved in mtRNA metabolism and editing can be silenced, we provide support for the view that ATP6 is encoded in the mt genome of Trypanosoma species and that it is incorporated into complex V. The reduction of the F1FO oligomer of complex V coincides with the accumulation of the F1 moiety in ATP6-lacking cells, which also appear to lack the FO ATP9 multimeric ring. The oligomycin sensitivity of ATPase activity of complex V in ATP6-lacking cells is reduced, reflecting the insensitivity of the Dk and Ak cells to this drug. In addition, the F1 moiety of complex V appears to exist as a dimer in steady state conditions and contains the ATP4 subunit traditionally assigned to the FO sub-complex.