UMPS (human) — review notes

UniProtKB:P11172, HGNC:12563. Bifunctional uridine 5'-monophosphate synthase (UMP synthase).
Deep research: falcon provider is out of credits (HTTP 402); no -deep-research-falcon.md. Review grounded in
UMPS-uniprot.txt, seeded GOA, and cached publications/PMID_*.md.

Core biology

UMP synthase catalyzes the final two steps of de novo pyrimidine biosynthesis on a single
polypeptide (bifunctional / multifunctional enzyme):

1. Orotate phosphoribosyltransferase (OPRT; EC 2.4.2.10) — N-terminal domain (residues ~2–214):
   condenses orotate + PRPP -> orotidine-5'-monophosphate (OMP) + PPi.
2. Orotidine-5'-phosphate decarboxylase (ODC / OMPdecase; EC 4.1.1.23) — C-terminal domain
   (residues ~221–480): decarboxylates OMP -> uridine monophosphate (UMP) + CO2.

UMP is the parent pyrimidine ribonucleotide; all other pyrimidine nucleotides (UDP, UTP, CTP, dCTP,
dTTP) derive from UMP via downstream kinases/synthases, not by UMPS itself.

• Bifunctional / single polypeptide: PMID:9042911; PMID:6893554.
• Structural / mechanistic (C-terminal OMPD, active site D312/K314/D317, covalent mechanism, homodimer): PMID:18184586. UniProt: "Homodimer; dimerization is required for enzymatic activity."
• Assay of both activities as a bifunctional protein: PMID:11730338.

Localization

Cytosolic enzyme (Reactome R-HSA-73564, R-HSA-73567; UniProt cytoplasm). A minor nuclear pool is
reported alongside CAD: PMID:15890648. Catalysis is cytosolic; nucleus kept as non-core.

Disease

Orotic aciduria 1 (ORAC1, MIM:258900): autosomal recessive; megaloblastic anemia, failure to thrive,
massive urinary orotic acid excretion; uridine-responsive. ORAC1 missense variants (R96G, V109G, G429R)
reduce OPRT and/or ODC activity: PMID:9042911.

Annotation decisions (summary)

• OPRT (GO:0004588) + ODC (GO:0004590) MF, all evidence codes -> ACCEPT (core; both are the defining activities).
• UMP biosynthetic process (GO:0006222) and 'de novo' UMP biosynthetic process (GO:0044205) -> ACCEPT (core BP).
• 'de novo' pyrimidine nucleobase biosynthetic (GO:0006207) -> ACCEPT (correct, slightly broader parent).
• pyrimidine nucleotide biosynthetic (GO:0006221) and pyrimidine nucleobase biosynthetic (GO:0019856) -> KEEP_AS_NON_CORE (correct but broad grouping terms).
• UDP biosynthetic process (GO:0006225) and 'de novo' CTP biosynthetic process (GO:0044210) -> REMOVE. Both are IEA Ensembl-Compara ortholog transfers (GO_REF:0000107) that mis-state the product: UMPS makes UMP, not UDP or CTP. These are over-propagated electronic inferences arguable on biochemical grounds.
• cytosol (GO:0005829) TAS x2, cytoplasm (GO:0005737) IDA -> ACCEPT.
• nucleus (GO:0005634) IDA -> KEEP_AS_NON_CORE (minor pool; not the site of the de novo pyrimidine reactions).
• protein binding (GO:0005515) IPI x2 (both with EPHA4/P54764, from BioPlex AP-MS) -> MARK_AS_OVER_ANNOTATED (bare protein binding; uninformative; not removed per policy).