NOA1 (nitric oxide associated 1) is a mitochondrial GTPase essential for mitochondrial ribosome biogenesis and protein synthesis. The protein localizes to the mitochondrial matrix where it associates with the inner mitochondrial membrane 1 and is required for assembly of the mitochondrial small ribosomal subunit 2. NOA1 knockout mice exhibit midgestation lethality with severe developmental defects, and NOA1-deficient cells show impaired mitochondrial protein synthesis and global oxidative phosphorylation defects 2. The protein's GTPase activity is stimulated by ribosomal constituents, supporting its role in mitoribosomal biogenesis 2. Notably, NOA1 follows an unexpected cellular trafficking pathway, first importing into the nucleus and nucleolus before export and mitochondrial import 3. NOA1 interacts with Complex I of the electron transport chain and DAP3, regulating both mitochondrial respiration and apoptosis 1. Knockdown of NOA1 reduces mitochondrial oxygen consumption and renders cells resistant to apoptotic stimuli 1. The protein is transcriptionally regulated in an oxygen-dependent manner and is involved in adjusting oxidative phosphorylation activity to oxygen availability 4. Additionally, NOA1 serves as a substrate for the mitochondrial ClpXP protease complex 3 and contains a caspase cleavage motif 5.