Affinage

NOA1

Nitric oxide-associated protein 1 · UniProt Q8NC60

Length
698 aa
Mass
78.5 kDa
Annotated
2026-04-29
15 papers in source corpus 9 papers cited in narrative 9 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

NOA1 (C4orf14) is a nuclear-encoded mitochondrial matrix GTPase that functions as an assembly factor for the small (28S) subunit of the mitochondrial ribosome, thereby supporting mitochondrial protein synthesis and oxidative phosphorylation. NOA1 co-purifies with the mt-SSU in a manner dependent on its GTPase activity and GTP binding, and its GTPase is stimulated by G-quadruplex RNA ligands binding to its C-terminal RNA-binding domain; loss of NOA1 depletes small subunit components, impairs mitochondrial translation, and causes a global OXPHOS defect with reduced Complex I- and Complex IV-dependent respiration (PMID:21118999, PMID:22447445, PMID:23933583). NOA1 also interacts with Complex I, Complex IV, the prohibitin complex, and DAP3, linking it to regulation of respiration and apoptosis sensitivity (PMID:19103604, PMID:21771794). Newly synthesized NOA1 first transits through the nucleolus—where it interacts with UBF1—before Crm1-dependent nuclear export and mitochondrial import; within mitochondria it is turned over by the ClpXP protease, and its mRNA is subject to WTAP-mediated m6A methylation that modulates its expression levels (PMID:25072814, PMID:39744575).

Mechanistic history

Synthesis pass · year-by-year structured walk · 8 steps
  1. 2008 High

    Identification of NOA1 as a mitochondrial GTPase interacting with Complex I and DAP3 established that it functions at the interface of respiration and apoptosis, revealing that its loss reduces O₂ consumption and confers apoptosis resistance.

    Evidence Immunoprecipitation-MS, mitochondrial subfractionation, knockdown with O₂ consumption and apoptosis assays in human cells

    PMID:19103604

    Open questions at the time
    • Mechanism by which NOA1 supports Complex I activity not defined
    • Whether the apoptosis phenotype is secondary to respiratory defect was not resolved
    • No ribosomal association yet tested
  2. 2010 High

    Knockout studies demonstrated that NOA1 is essential for mitochondrial protein synthesis and mitoribosome assembly, shifting the functional model from a respiratory chain accessory to a translation/ribosome biogenesis factor.

    Evidence NOA1-knockout MEFs analyzed by sucrose gradient sedimentation, mitochondrial translation assay, and in vitro GTPase stimulation by bacterial ribosomal constituents

    PMID:21118999

    Open questions at the time
    • Which mitoribosomal subunit NOA1 associates with was not resolved
    • Whether GTPase activity is required for ribosome interaction was untested
  3. 2011 High

    Demonstration that NOA1 resides in the mitochondrial matrix and interacts with Complex IV and the prohibitin complex broadened its interaction network beyond Complex I and linked its expression to oxygen-sensitive transcriptional control.

    Evidence Native PAGE/BN-PAGE, Co-IP, knockdown with respiratory complex activity assays, oxygen-dependent transcription analysis in mouse cells

    PMID:21771794

    Open questions at the time
    • Whether interactions with Complex IV and prohibitin are direct or mediated through mt-SSU was unclear
    • Molecular basis of oxygen-sensitive regulation not defined
  4. 2012 High

    Co-purification with the 28S mt-SSU and GTPase-dependent interaction pinpointed NOA1 as a small subunit assembly factor, and studies in yeast (Mtg3) showed it promotes 15S rRNA processing during mt-SSU maturation.

    Evidence Recombinant protein co-purification, sucrose gradients, GTPase mutant analysis, siRNA knockdown, Northern blotting of rRNA processing, Mrpl4p genetic rescue in yeast

    PMID:22447445 PMID:22621929

    Open questions at the time
    • Structural basis of NOA1–mt-SSU interaction unknown
    • Whether rRNA processing role is conserved from yeast to mammals not tested
  5. 2013 Medium

    Discovery that G-quadruplex RNA stimulates NOA1 GTPase activity provided a candidate regulatory mechanism coupling RNA recognition to the GTP hydrolysis cycle during ribosome assembly.

    Evidence SELEX with recombinant NOA1 and GTPase mutant K353R, in vitro GTPase stimulation assay

    PMID:23933583

    Open questions at the time
    • Physiological G-quadruplex-forming RNA partner in mitochondria not identified
    • In vivo relevance of G-quadruplex stimulation not demonstrated
    • Single-lab biochemical study
  6. 2014 High

    Characterization of NOA1's nucleolar transit via Crm1-dependent export before mitochondrial import, its interaction with UBF1, and its degradation by ClpXP revealed a multi-compartment trafficking pathway and a quality-control mechanism for the protein.

    Evidence Live-cell imaging, NLS/NES/MTS mutagenesis, leptomycin B treatment, Co-IP for UBF1, in vitro ClpXP degradation assay, caspase activity assay

    PMID:25072814

    Open questions at the time
    • Functional significance of nucleolar transit and UBF1 interaction for mitoribosome assembly unknown
    • Signals that trigger ClpXP-mediated turnover not identified
  7. 2024 Medium

    Dissection of Mtg3 domains in yeast showed that C-terminal domain mediates mitoribosome binding while GTPase activity is dispensable for association but essential for function, supporting a model in which GTP/GDP cycling drives a conformational checkpoint during mt-SSU maturation.

    Evidence C-terminal deletion and GTPase point mutagenesis with sucrose gradient and respiratory growth assays in yeast

    PMID:39180962

    Open questions at the time
    • Whether this domain architecture model applies to human NOA1 not tested
    • Nature of the conformational change or checkpoint not structurally resolved
    • Single study in yeast ortholog
  8. 2025 Medium

    Identification of WTAP-mediated m6A modification of NOA1 mRNA as a regulatory input controlling NOA1 protein levels and mitochondrial integrity added an epitranscriptomic layer to NOA1 regulation.

    Evidence MeRIP-qPCR, WTAP knockdown/overexpression, electron microscopy, Western blot in hepatoma cells

    PMID:39744575

    Open questions at the time
    • Whether m6A affects NOA1 mRNA stability or translation efficiency not distinguished
    • Mitochondrial phenotype attributed to NOA1 but other WTAP targets not excluded
    • Single cell-line study

Open questions

Synthesis pass · forward-looking unresolved questions
  • A high-resolution structural model of NOA1 bound to the human mt-SSU is lacking, and the in vivo RNA ligand(s) that regulate its GTPase cycle during mitoribosome assembly remain unidentified.
  • No cryo-EM or crystal structure of NOA1–mt-SSU complex
  • Physiological G-quadruplex RNA partner not identified in human mitochondria
  • Functional significance of nucleolar transit remains mechanistically unexplained

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0003924 GTPase activity 5 GO:0003677 DNA binding 1 GO:0003723 RNA binding 1
Localization
GO:0005739 mitochondrion 5 GO:0005730 nucleolus 1
Pathway
GO:0005840 ribosome 4 R-HSA-392499 Metabolism of proteins 3 R-HSA-1430728 Metabolism 2 R-HSA-5357801 Programmed Cell Death 2
Partners
CLPPCLPXDAP3MRPL4MT-ND1PHBUBF1
Complex memberships
mitochondrial small ribosomal subunit (28S/mt-SSU)

Evidence

Reading pass · 9 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2008 hNOA1 is a large mitochondrial GTPase peripherally associated with the inner mitochondrial membrane facing the matrix; it interacts with Complex I of the electron transport chain and DAP3 (death-associated protein 3); knockdown reduces mitochondrial O2 consumption ~20% in a Complex I-dependent manner and renders cells more resistant to apoptotic stimuli (gamma-interferon, staurosporine). Immunofluorescence, immunoelectron microscopy, mitochondrial subfractionation, immunoprecipitation-mass spectrometry, knockdown with O2 consumption assay and apoptosis assay The Journal of biological chemistry High 19103604
2010 NOA1 is an essential mitochondrial GTPase required for mitochondrial protein synthesis; NOA1-deficient mouse embryonic fibroblasts show deficient mitochondrial translation, global OXPHOS defect, impaired staurosporine-induced apoptosis, and anomalous sedimentation of mitochondrial ribosomal subunits consistent with defective mitoribosome assembly; intrinsic NOA1 GTPase activity is stimulated by bacterial ribosomal constituents in vitro. Knockout mouse generation, sucrose gradient centrifugation, Western blotting, in vitro GTPase activity assay with ribosomal constituents, mitochondrial protein synthesis assay Molecular biology of the cell High 21118999
2011 mNOA1 is located mostly in the mitochondrial matrix where it interacts with high molecular mass complexes including Complex IV of the respiratory chain and the prohibitin complex; knockdown impaired enzyme activity I+III, resulting in oxidative stress and cell death; mNOA1 is transcriptionally regulated in an oxygen-sensitive manner, adjusting OXPHOS activity to oxygen availability. Mitochondrial subfractionation, native PAGE/BN-PAGE complex analysis, immunoprecipitation, knockdown with respiratory complex activity assay and cell viability assay, oxygen-dependent transcription analysis The Journal of biological chemistry High 21771794
2012 Human C4orf14 (NOA1) co-purifies with the small 28S subunit of the mitochondrial ribosome; gene silencing specifically affects small subunit components and decreases mitochondrial protein synthesis; the GTPase activity of C4orf14 and GTP binding are critical for its interaction with the 28S subunit; C4orf14 is associated with mitochondrial nucleoids and its silencing causes mitochondrial DNA depletion; in vitro C4orf14 binds DNA directly. Co-purification of recombinant protein, sucrose gradient fractionation, siRNA knockdown with Western blotting and mitochondrial translation assay, GTPase mutant analysis, in vitro DNA-binding assay, mitochondrial DNA quantification Nucleic acids research High 22447445
2013 NOA1 binds specifically to G-quadruplex-forming oligonucleotides via its RNA-binding domain; binding of G-quadruplex oligonucleotides stimulates the GTPase activity of NOA1, establishing a regulatory link between G-quadruplex-containing RNAs and NOA1 function in mitochondrial ribosome assembly. SELEX with recombinant wildtype and GTPase mutant (K353R) NOA1, GTPase activity assay with G-quadruplex oligonucleotides Biochimica et biophysica acta Medium 23933583
2014 Newly translated NOA1 is first imported into the nucleus where it localizes to the nucleolus and interacts with UBF1, before nuclear export via a Crm1/leptomycin-B-sensitive NES and import into mitochondria; mutation of the NLS prevents both nuclear and mitochondrial import; deletion of the MTS or C-terminal RNA-binding domain impairs mitochondrial import; absence of MTS causes nuclear accumulation and increased caspase-dependent apoptosis; NOA1 is a substrate of the mitochondrial matrix protease ClpXP. Fluorescence microscopy (live imaging), NLS/NES/MTS mutagenesis, leptomycin-B treatment, co-immunoprecipitation (UBF1 interaction), ClpXP in vitro degradation assay, caspase activity assay PloS one High 25072814
2025 WTAP regulates m6A methylation of NOA1 mRNA; knockdown of WTAP in hepatoma cells induces mitochondrial damage (smaller mitochondria, compressed intermembrane space, low mitochondrial membrane potential) associated with altered NOA1 expression, establishing WTAP as a writer that controls NOA1 levels via m6A modification. MeRIP-qPCR, WTAP knockdown/overexpression, electron microscopy, Western blot, mass spectrometry Journal of Cancer Medium 39744575
2012 Mtg3 (yeast ortholog of NOA1) is required for assembly of the small (30S) mitochondrial ribosomal subunit; mtg3 mutations cause accumulation of the 15S rRNA precursor with an 80-nt 5' extension; overexpression of Mrpl4p (a 54S constituent at the peptide exit site) partially rescues the mtg3 null respiratory defect with increased processed 15S rRNA, indicating Mtg3p and Mrpl4p jointly regulate small subunit assembly by modulating 15S rRNA processing. Sucrose gradient sedimentation, immunoblotting with subunit-specific antibodies, Northern blotting (rRNA processing), genetic rescue by Mrpl4p overexpression The Journal of biological chemistry High 22621929
2024 Mtg3 (yeast ortholog of NOA1) requires its C-terminal domain for robust binding to the mitoribosome small subunit; point mutations abrogating GTP/GDP binding and GTPase activity impair protein function in vivo but do not compromise mitoribosome association, supporting a model where Mtg3 binds via its C-terminus and uses GTP/GDP cycling to facilitate a conformational change or validate a folding intermediate during small subunit maturation. Sucrose density gradient analysis of mitoribosome association, C-terminal deletion and point mutagenesis, in vivo respiratory growth assays Biochemical and biophysical research communications Medium 39180962

Source papers

Stage 0 corpus · 15 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2013 Roles of NIA/NR/NOA1-dependent nitric oxide production and HY1 expression in the modulation of Arabidopsis salt tolerance. Journal of experimental botany 90 23744476
2012 Human C4orf14 interacts with the mitochondrial nucleoid and is involved in the biogenesis of the small mitochondrial ribosomal subunit. Nucleic acids research 77 22447445
2010 NOA1 is an essential GTPase required for mitochondrial protein synthesis. Molecular biology of the cell 56 21118999
2008 hNOA1 interacts with complex I and DAP3 and regulates mitochondrial respiration and apoptosis. The Journal of biological chemistry 43 19103604
2011 Nitric oxide accumulation in Arabidopsis is independent of NOA1 in the presence of sucrose. The Plant journal : for cell and molecular biology 40 21689173
2011 NOA1 functions in a temperature-dependent manner to regulate chlorophyll biosynthesis and Rubisco formation in rice. PloS one 31 21625436
2014 NOA1, a novel ClpXP substrate, takes an unexpected nuclear detour prior to mitochondrial import. PloS one 28 25072814
2011 Nitric oxide-associated protein 1 (NOA1) is necessary for oxygen-dependent regulation of mitochondrial respiratory complexes. The Journal of biological chemistry 25 21771794
2012 The putative GTPase encoded by MTG3 functions in a novel pathway for regulating assembly of the small subunit of yeast mitochondrial ribosomes. The Journal of biological chemistry 21 22621929
2011 Silencing NOA1 elevates herbivory-induced jasmonic acid accumulation and compromises most of the carbon-based defense metabolites in Nicotiana attenuata(F). Journal of integrative plant biology 20 21457460
2013 Binding to G-quadruplex RNA activates the mitochondrial GTPase NOA1. Biochimica et biophysica acta 14 23933583
2013 TNFRSF10A-LOC389641 rs13278062 but not REST-C4orf14-POLR2B-IGFBP7 rs1713985 was found associated with age-related macular degeneration in a Chinese population. Investigative ophthalmology & visual science 13 24235014
2014 Cloning of nitric oxide associated 1 (NOA1) transcript from oil palm (Elaeis guineensis) and its expression during Ganoderma infection. Journal of plant physiology 10 25462975
2025 WTAP regulates Mitochondrial damage and Lipid oxidation in HCC by NOA1 mediated m6A modification. Journal of Cancer 6 39744575
2024 Insights into Mtg3-mitochondrial ribosome association in Saccharomyces cerevisiae. Biochemical and biophysical research communications 0 39180962