SARS2

SARS2 encodes the mitochondrial seryl-tRNA synthetase, an aminoacyl-tRNA charging enzyme required for mitochondrial protein synthesis and respiratory function, whose loss of function causes mitochondrial disease (PMID:33751860, PMID:42220212). The gene is transcribed from a bidirectional promoter shared with MRPS12 that is controlled by an array of four CCAAT boxes bound by transcription factor NF-Y, which adopts alternate configurations dictating directional transcriptional selectivity toward the SARS2 (SARSM) direction (PMID:18755224, PMID:19439209). This promoter integrates mitochondrial stress signals: prolonged mitochondrial stress produces dose-dependent, CCAAT-box-dependent bidirectional suppression, whereas pre-treatment conditions drive CCAAT-box-independent stimulation correlated with mitochondrial ROS (PMID:18755224). Compound heterozygous missense variants in SARS2 cause HUPRA syndrome, establishing that biallelic loss of function of this enzyme is sufficient for disease (PMID:33751860). Pathogenic variants act through at least two distinct, variant-dependent mechanisms: most impair mitochondrial oxygen consumption to differing degrees, while exon-13 missense variants including the common R402H allele instead reduce exon 13 inclusion during pre-mRNA splicing, causing loss of function without direct protein dysfunction (PMID:42220212).

1. 2001 Low

   Before SARS2's disease relevance was known, it was tested as a candidate for DFNA4-linked deafness to determine whether coding-region mutations underlie that phenotype; the negative result excluded SARS2 structural mutations as the cause in those families.

   Evidence Direct sequencing of coding regions, UTRs, and splice junctions in deafness families and controls

   PMID:11317363

   Open questions at the time

   • Negative finding only; does not address SARS2 function
   • Does not exclude regulatory or non-coding contributions
2. 2008 Medium

   To understand how SARS2 expression is set, the bidirectional MRPS12/SARSM promoter was dissected, establishing that a CCAAT-box array bound by NF-Y governs transcription and that the promoter responds bidirectionally to mitochondrial stress.

   Evidence Reporter gene assays with mutated promoter constructs in multiple human and mouse cell lines under mitochondrial toxin treatment

   PMID:18755224

   Open questions at the time

   • Stress responses differ by cell type and timing
   • Stimulatory response operates independently of the mapped CCAAT/NRF-2/AP-1 sites, leaving its mediator undefined
3. 2009 Medium

   To resolve how a shared promoter achieves directional output, NF-Y binding configurations across the CCAAT array were mapped, showing combinatorial, non-additive control biased toward the SARSM direction.

   Evidence EMSA, permutation reporter constructs, and wild-type/dominant-negative NF-Y overexpression in human and mouse cells

   PMID:19439209

   Open questions at the time

   • Mechanistic basis of alternate NF-Y configurations not structurally defined
   • Connection between directional selectivity and physiological MRPS12:SARS2 stoichiometry untested
4. 2021 Low

   To extend the pathogenic variant spectrum, compound heterozygous SARS2 variants were identified in a HUPRA syndrome case, demonstrating that biallelic loss of function of the enzyme is sufficient to cause the disease.

   Evidence Whole-exome and Sanger sequencing with bioinformatic and structural pathogenicity prediction

   PMID:33751860

   Open questions at the time

   • Single case
   • Variant effect predicted computationally without direct enzymatic assay
5. 2022 Low

   To test whether SARS2 dosage modifies an unrelated neurodegenerative disease, a chromosome 19 locus containing SARS2 was linked to age at onset in SPG4, with the risk allele correlating with higher SARS2 protein in earlier-onset patients.

   Evidence GWAS plus Western blotting in patient lymphocytes

   PMID:36056923

   Open questions at the time

   • Correlative; no functional validation that SARS2 levels causally alter SPG4 onset
   • Locus contains other genes; SARS2 causality not isolated
6. 2026 Medium

   To explain why pathogenic SARS2 variants produce heterogeneous outcomes, an allelic series resolved two distinct loss-of-function mechanisms—graded impairment of mitochondrial respiration versus disrupted exon 13 splicing for the common R402H and D390G alleles.

   Evidence Oxygen consumption rate assays, computational splicing prediction, and functional exon-inclusion splicing assays across 11 variants

   PMID:42220212

   Open questions at the time

   • Direct aminoacylation activity not measured per variant
   • Tissue-specific consequences of splicing defect not characterized

• How SARS2 transcriptional regulation, aminoacylation activity, and splicing fidelity integrate to set tissue-specific disease severity remains unresolved.
• No structural model of the enzyme with its tRNA substrate in the corpus
• Link between NF-Y-driven expression level and variant pathogenicity untested
• Genotype-phenotype map across HUPRA, SPG4, and other presentations incomplete