Impaired ATP synthase assembly associated with a mutation in the human ATPsynthase subunit 6 gene

Mutations in human mitochondrial DNA are a well recognized cause of disease . A mutation at nucleotide position 8993 of human mitochondrial DNA, locate d within the gene for ATP synthase subunit 6, is associated with the neurol ogical muscle weakness, ataxia, and retinitis pigmentosa (NARP) syndrome. T o enable analysis of this mutation in control nuclear backgrounds, two diff erent cell lines were transformed with mitochondria carrying NARP mutant mi tochondrial DNA. Transformant cell lines had decreased ATP synthesis capaci ty, and many also had abnormally high levels of two ATP synthase sub-comple xes, one of which was F-1-ATPase. A combination of metabolic labeling and i mmunoblotting experiments indicated that assembly of ATP synthase was slowe d and that the assembled holoenzyme was unstable in cells carrying NARP mut ant mitochondrial DNA compared with control cells. These findings indicate that altered assembly and stability of ATP synthase are underlying molecula r defects associated with the NARP mutation in subunit 6 of ATP synthase, y et intrinsic enzyme activity is also compromised.