The intricate structure of mitochondrial membranes supports efficient ATP synthesis through oxidative phosphorylation. Weissman, Nunnari and colleagues construct a quantitative genetic interaction map of yeast mitochondria, called the MITO-MAP, that reveals insights into the organization of this organelle (J. Cell Biol. 195, 323–340; 2011).

The MITO-MAP was constructed by analysing pair-wise genetic interactions between 1,482 yeast genes. Importantly, although many previously unappreciated interactions were identified in this study, the data set was consistent with other published small-scale interaction networks in yeast. With the MITO-MAP as a guide, the authors uncovered a six-member protein complex termed MitOS (Fcj1, Aim5, Aim13, Aim37, Mos1 and Mos2) that links the mitochondrial outer and inner membranes. Subsequent microscopy revealed that MitOS components assemble into heterogenous structures on the inner membrane.

Deleting members of MitOS induced defects in mitochondrial inner-membrane structure and cristae junctions. The authors identified genetic interactions between MitOS and ATP synthase, and propose that ATP synthase is necessary for MitOS-dependent regulation of inner mitochondrial membrane structure. Future studies will help resolve the precise function of MitOS in inner membrane organisation, but the MITO-MAP remains a rich resource for understanding mitochondrial structure and function.