Om45 is a major protein of the yeast outer mitochondrial membrane under
respiratory conditions. However, the cellular role of the protein has
remained obscure. Previously, deletion mutant phenotypes have not been
found, and clear amino acid sequence similarities that would allow
inferring its functional role are not available. In this work, we
describe synthetic petite mutants of UGO1 and GEM1 that depend on the
presence of OM45 for respiratory growth, as well as the identification
of several multicopy suppressors of the synthetic petite phenotypes. In
the analysis of our mutants, we demonstrate that Om45 and Gem1 have a
collaborative role in the maintenance of mitochondrial morphology,
cristae structure, and mitochondrial DNA maintenance. A group of
multicopy suppressors rescuing the synthetic lethal phenotypes of the
mutants on non-fermentable carbon sources additionally supports this
result. Our results imply that the synthetic petite phenotypes we
observed are due to the disturbance of the inner mitochondrial membrane
and point to this mitochondrial sub-compartment as the main target of
action of Om45, Ugo1, and the yeast Miro GTPase Gem1.