biostudies-literatureLe Vasseur MHoward Hughes Medical InstituteNational Heart, Lung, and Blood InstituteNational Institutes of HealthNational Institute of General Medical SciencesNational Human Genome Research Institutee67624https://www.ebi.ac.uk/biostudies/studies/S-EPMC8154037biostudies-literatureUnknown10Dysfunction of the mitochondrial electron transport chain (mETC) is a major cause of human mitochondrial diseases. To identify determinants of mETC function, we screened a genome-wide human CRISPRi library under oxidative metabolic conditions with selective inhibition of mitochondrial Complex III and identified ovarian carcinoma immunoreactive antigen (OCIA) domain-containing protein 1 (OCIAD1) as a Complex III assembly factor. We find that OCIAD1 is an inner mitochondrial membrane protein that forms a complex with supramolecular prohibitin assemblies. Our data indicate that OCIAD1 is required for maintenance of normal steady-state levels of Complex III and the proteolytic processing of the catalytic subunit cytochrome c1 (CYC1). In OCIAD1 depleted mitochondria, unprocessed CYC1 is hemylateLifeGenome-wide CRISPRi screening identifies OCIAD1 as a prohibitin client and regulatory determinant of mitochondrial Complex III assembly in human cells.PMC8154037K99HL133372R01GM126081K99GM130964S100D018223HHMIR00HL1333721RM1HG009490R37GM097432Le Vasseur MYamada JFriedman JPhinney BSNunnari JJost MHorlbeck MAWeissman JSKampmann MXu JSalemi MRfalseGenome-wide CRISPRi screening identifies OCIAD1 as a prohibitin client and regulatory determinant of mitochondrial Complex III assembly in human cells.Dysfunction of the mitochondrial electron transport chain (mETC) is a major cause of human mitochondrial diseases. To identify determinants of mETC function, we screened a genome-wide human CRISPRi library under oxidative metabolic conditions with selective inhibition of mitochondrial Complex III and identified ovarian carcinoma immunoreactive antigen (OCIA) domain-containing protein 1 (OCIAD1) as a Complex III assembly factor. We find that OCIAD1 is an inner mitochondrial membrane protein that forms a complex with supramolecular prohibitin assemblies. Our data indicate that OCIAD1 is required for maintenance of normal steady-state levels of Complex III and the proteolytic processing of the catalytic subunit cytochrome c1 (CYC1). In OCIAD1 depleted mitochondria, unprocessed CYC1 is hemylat2021-01-01T00:00:00Z2021 May2025-04-04T10:18:17.876Z2025-04-04T10:18:17.876ZS-EPMC81540373403485910.7554/eLife.67624