Antimycin A resistance in a mutant Leishmania tarentolae strain is correlated to a point mutation in the mitochondrial apocytochrome b gene.

In this paper we report the first case of antimycin A resistance in a protozoan parasite that is attributable to a mutation in the mitochondrial apocytochrome b (CYb) gene. We selected for, and isolated, a mutant Leishmania tarentolae strain that is resistant to antimycin A. This resistance was evident at the levels of the in vitro growth and enzymatic activity of the cytochrome bc1 complex. Molecular characterisation of the mutant revealed a Ser35Ile mutation in the expected region of the CYb gene. In kinetoplastids, CYb and other structural genes of the mitochondrial genome are located on the maxicircle component of the mitochondrial DNA, which is present in 20-50 copies. Primer-extension analysis confirmed the presence of the mutation at the mRNA level. The phenotypic manifestation of the mutation implies that the CYb mRNA is edited and translated within the mitochondrion. Thus, this finding provides direct evidence that edited RNAs are translated in kinetoplastid mitochondria. Furthermore, a defined mutation conferring drug resistance to a mitochondrial gene product can be exploited for the development of mitochondrial transfection systems for trypanosomatids.