Affinage

NOA1

Nitric oxide-associated protein 1 · UniProt Q8NC60

Length
698 aa
Mass
78.5 kDa
Annotated
2026-06-10
13 papers in source corpus 9 papers cited in narrative 9 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 7/7 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

NOA1 is an evolutionarily conserved mitochondrial GTPase essential for biogenesis of the small mitochondrial ribosomal subunit and, consequently, for mitochondrial protein synthesis and oxidative phosphorylation (PMID:21118999, PMID:22447445). It is peripherally associated with the matrix face of the inner mitochondrial membrane and co-purifies with the 28S small subunit, an interaction that requires both bound GTP and intrinsic GTPase activity (PMID:22447445, PMID:19103604). Loss of NOA1 produces anomalous sedimentation of mitochondrial ribosomal subunits, deficient mitochondrial translation, and a global OXPHOS defect (PMID:21118999, PMID:22447445). Work in the yeast ortholog Mtg3 defines this role genetically: Mtg3 is specifically required for 30S small subunit assembly through processing of the 15S rRNA precursor, and it engages precursor mitoribosomes via its C-terminal domain while GTP/GDP cycling drives a conformational step rather than the initial binding event (PMID:22621929, PMID:39180962). Beyond ribosome assembly, NOA1 interacts with respiratory chain complexes and DAP3 to modulate respiration and apoptosis, with knockdown reducing Complex I-dependent O2 consumption and altering sensitivity to apoptotic stimuli (PMID:19103604, PMID:21771794). Its GTPase activity is stimulated in vitro by bacterial ribosomal constituents and by G-quadruplex-forming oligonucleotides, linking nucleic acid ligands to NOA1 enzymatic regulation (PMID:21118999, PMID:23933583). Newly translated NOA1 undergoes an obligatory nucleolar transit, interacting with UBF1 and exiting via a CRM1-dependent NES before mitochondrial import, after which it is subject to ClpXP-mediated proteolysis (PMID:25072814).

Mechanistic history

Synthesis pass · year-by-year structured walk · 9 steps
  1. 2008 High

    Established NOA1 as a matrix-facing inner-membrane protein physically linked to respiration and apoptosis, raising the question of whether it acts directly on the electron transport chain.

    Evidence Immunofluorescence/immuno-EM localization, IP-MS interaction mapping, and siRNA knockdown with O2 consumption and apoptosis assays in human cells

    PMID:19103604

    Open questions at the time
    • Did not resolve whether the respiration defect is a direct Complex I effect or secondary to a translation defect
    • DAP3 interaction not mechanistically dissected
  2. 2010 High

    Demonstrated that NOA1 is required for mitochondrial protein synthesis and ribosome assembly, reframing its respiratory phenotype as downstream of a translation defect.

    Evidence Knockout mouse, sucrose gradient fractionation of mitoribosomal subunits, and in vitro GTPase assay stimulated by bacterial ribosomal constituents

    PMID:21118999

    Open questions at the time
    • Did not identify which subunit NOA1 acts on or the GTP-dependence of subunit binding
    • Physiological GTPase stimulator in mitochondria not defined
  3. 2011 Medium

    Localized mouse NOA1 to the matrix and tied its loss to respiratory complex dysfunction and oxidative stress, while noting oxygen-sensitive transcriptional control.

    Evidence Mitochondrial fractionation, blue-native interaction analysis with Complex IV and prohibitin, and siRNA knockdown with enzyme-activity and oxidative-stress readouts

    PMID:21771794

    Open questions at the time
    • Complex IV and prohibitin associations not validated as direct stable partners
    • Relationship between these complex associations and ribosome assembly unresolved
  4. 2012 High

    Pinpointed NOA1 to the 28S small subunit and showed GTP and GTPase activity are required for that interaction, while implicating it in nucleoid/mtDNA maintenance.

    Evidence Co-purification, sucrose gradient fractionation, siRNA, in vitro DNA binding, and IP with mitochondrial translation factors in human cells

    PMID:22447445

    Open questions at the time
    • Whether DNA binding/mtDNA depletion is a direct role or secondary to translation loss unresolved
    • Structural basis of GTP-dependent 28S engagement not determined
  5. 2012 High

    Defined the assembly step genetically in the yeast ortholog Mtg3, linking it specifically to small-subunit biogenesis via 15S rRNA precursor processing.

    Evidence Genetic screen, sucrose gradient sedimentation, Northern blot for rRNA precursors, and genetic rescue by Mrpl4p overexpression in yeast

    PMID:22621929

    Open questions at the time
    • Mechanism connecting Mtg3 to the rRNA processing machinery not defined
    • Direct enzymatic role in processing versus chaperone role for assembly unresolved
  6. 2013 Medium

    Identified G-quadruplex RNAs/oligonucleotides as ligands that bind and stimulate NOA1 GTPase activity, proposing a nucleic-acid-based regulatory input.

    Evidence SELEX with recombinant wildtype and GTPase-mutant NOA1 plus GTPase activity assay with G-quadruplex oligonucleotides

    PMID:23933583

    Open questions at the time
    • Endogenous G-quadruplex RNA target in mitochondria not identified
    • In vitro stimulation not linked to ribosome assembly in cells
  7. 2014 Medium

    Revealed an unexpected obligatory nucleolar transit and CRM1-dependent export route preceding mitochondrial import, and identified ClpXP as the protease degrading NOA1.

    Evidence Live-cell imaging of NLS/NES/MTS mutants, leptomycin-B inhibition, ClpXP substrate assay, and co-IP with UBF1

    PMID:25072814

    Open questions at the time
    • Functional purpose of the nucleolar UBF1 interaction unknown
    • Whether nuclear transit is universal across cell types not established
  8. 2024 Medium

    Separated mitoribosome binding from nucleotide cycling in Mtg3, showing the C-terminus mediates binding while GTP/GDP cycling drives a downstream conformational/maturation step.

    Evidence Sucrose density gradient fractionation, C-terminal deletion and GTPase active-site point mutants, and in vivo complementation in yeast

    PMID:39180962

    Open questions at the time
    • The conformational change or folding-validation step is inferred, not directly observed
    • Structural model of the C-terminal binding interface lacking
  9. 2025 Low

    Placed NOA1 mRNA as a target of WTAP-mediated m6A modification, linking an epitranscriptomic regulator to mitochondrial integrity.

    Evidence MeRIP-qPCR for m6A on NOA1, WTAP conditional knockout, electron microscopy of mitochondrial morphology, and MS identification

    PMID:39744575

    Open questions at the time
    • Direct causal link from m6A on NOA1 specifically to the mitochondrial phenotype not rigorously established; single lab, single study
    • Effect of the m6A mark on NOA1 translation or stability not measured

Open questions

Synthesis pass · forward-looking unresolved questions
  • How GTP hydrolysis is coupled to release of NOA1 from the maturing small subunit, and the structural basis of its assembly chaperone activity, remain unresolved.
  • No structure of NOA1 bound to the small subunit
  • The endogenous mitochondrial GTPase-stimulating ligand is undefined
  • The role of the nucleolar transit step is not functionally explained

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0003924 GTPase activity 4 GO:0003677 DNA binding 1 GO:0003723 RNA binding 1
Localization
GO:0005739 mitochondrion 4 GO:0005730 nucleolus 1
Pathway
R-HSA-8953854 Metabolism of RNA 3 R-HSA-1430728 Metabolism 2 R-HSA-1852241 Organelle biogenesis and maintenance 2
Complex memberships
small mitochondrial ribosomal subunit (28S/30S)

Evidence

Reading pass · 9 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2010 NOA1 (knockout mice and in vitro assays) is required for mitochondrial protein synthesis; NOA1-deficient cells show deficient mitochondrial protein synthesis, global OXPHOS defect, and anomalous sedimentation of mitochondrial ribosomal subunits consistent with a defect in mitochondrial ribosome assembly. In vitro, intrinsic NOA1 GTPase activity was stimulated by bacterial ribosomal constituents. Knockout mouse generation, sucrose gradient centrifugation of mitochondrial ribosomal subunits, Western blotting, in vitro GTPase activity assay with ribosomal constituents Molecular biology of the cell High 21118999
2012 Human C4orf14 (NOA1) co-purifies with the small 28S mitochondrial ribosomal subunit and co-fractionates with it on sucrose gradients. Gene silencing specifically reduced components of the small subunit and decreased mitochondrial protein synthesis. The GTPase activity of C4orf14 and bound GTP were both critical for interaction with the 28S subunit. C4orf14 also associates with mitochondrial nucleoids and binds DNA in vitro; its silencing caused mitochondrial DNA depletion. Co-purification of recombinant C4orf14 from human cells, sucrose gradient fractionation, gene silencing (siRNA), in vitro DNA binding assay, immunoprecipitation with mitochondrial translation factors Nucleic acids research High 22447445
2008 hNOA1 is peripherally associated with the inner mitochondrial membrane facing the matrix. By immunoprecipitation-mass spectrometry, endogenous hNOA1 interacts with Complex I of the electron transport chain and with DAP3 (death-associated protein 3). Knockdown of hNOA1 reduces mitochondrial O2 consumption ~20% in a Complex I-dependent manner and renders cells more resistant to apoptotic stimuli (gamma-interferon and staurosporine). Immunofluorescence, immunoelectron microscopy, mitochondrial subfractionation, immunoprecipitation-mass spectrometry, siRNA knockdown with O2 consumption assay and apoptosis assay The Journal of biological chemistry High 19103604
2011 Mouse NOA1 (mNOA1) localizes predominantly in the mitochondrial matrix and interacts with several high-molecular-mass complexes, most notably Complex IV of the respiratory chain and the prohibitin complex. Knockdown of mNOA1 impaired enzyme activity of complexes I+III, resulting in oxidative stress and cell death. mNOA1 is transcriptionally regulated in an oxygen-sensitive manner. Mitochondrial fractionation, blue-native PAGE/interaction analysis, siRNA knockdown with enzyme activity assays and oxidative stress measurements The Journal of biological chemistry Medium 21771794
2013 NOA1 binds specifically to oligonucleotides that fold into G-quadruplex structures (identified by SELEX), and binding of G-quadruplex oligonucleotides stimulates the GTPase activity of NOA1, establishing a regulatory link between G-quadruplex-containing RNAs and NOA1 GTPase function. SELEX with recombinant wildtype NOA1 and GTPase mutant NOA1-K353R, GTPase activity assay with G-quadruplex oligonucleotides Biochimica et biophysica acta Medium 23933583
2014 Newly translated NOA1 is first imported into the nucleus (localizing to the nucleolus where it interacts with UBF1) before nuclear export (via a CRM1/leptomycin-B-sensitive NES) and subsequent import into mitochondria. Mutation of the nuclear localization signal (NLS) prevented both nuclear and mitochondrial import; deletion of the N-terminal mitochondrial targeting sequence (MTS) caused nuclear accumulation and increased caspase-dependent apoptosis. NOA1 is also a substrate of the mitochondrial matrix protease complex ClpXP. Live cell imaging/immunofluorescence of NLS/NES/MTS mutants, leptomycin-B inhibition, ClpXP substrate assay, co-immunoprecipitation with UBF1 PloS one Medium 25072814
2012 Yeast Mtg3 (NOA1 ortholog) is required for assembly of the mitochondrial 30S (small) ribosomal subunit but not the 54S (large) subunit. Mutations in MTG3 cause accumulation of a 15S rRNA precursor with an 80-nucleotide 5' extension. Overexpression of Mrpl4p (a 54S constituent at the peptide exit site) partially rescues the respiratory deficiency of mtg3 null mutants, accompanied by increased processed 15S rRNA, suggesting Mtg3p and Mrpl4p jointly regulate small subunit assembly by modulating 15S rRNA processing. Genetic screen, sucrose gradient sedimentation, immunoblotting with subunit-specific antibodies, Northern blot for rRNA precursors, genetic rescue by overexpression The Journal of biological chemistry High 22621929
2024 The C-terminal domain of yeast Mtg3 (NOA1 ortholog) is required for robust binding to the mitoribosome, as shown by sucrose density gradient analysis. Point mutants that abrogate GTP/GDP binding and GTPase activity compromise protein function in vivo, but surprisingly, mitoribosome association was not compromised in nucleotide-binding/hydrolysis-deficient mutants, supporting a model where Mtg3 binds precursor mitoribosomes through its C-terminus while GTP/GDP cycling drives a conformational change or validates a folding intermediate. Sucrose density gradient fractionation, C-terminal deletion mutants, point mutagenesis of GTPase active site, in vivo functional complementation assay Biochemical and biophysical research communications Medium 39180962
2025 WTAP regulates m6A methylation of NOA1 mRNA (confirmed by MeRIP-qPCR), and WTAP knockdown leads to mitochondrial damage (smaller mitochondria, compressed intermembrane space, reduced mitochondrial membrane potential), suggesting NOA1 is a downstream effector of WTAP-mediated m6A modification in maintaining mitochondrial integrity. MeRIP-qPCR for m6A methylation of NOA1, WTAP conditional knockout, electron microscopy for mitochondrial morphology, mass spectrometry identification of NOA1 as WTAP-related protein Journal of Cancer Low 39744575

Source papers

Stage 0 corpus · 13 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2012 Human C4orf14 interacts with the mitochondrial nucleoid and is involved in the biogenesis of the small mitochondrial ribosomal subunit. Nucleic acids research 78 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 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 14 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

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