spa1 (SPBC577.14c) — S. pombe ornithine decarboxylase antizyme — review notes

Deep-research note: the automated deep-research job
(scripts/deep_research_wrapper.py SCHPO spa1 falcon --fallback perplexity-lite)
produced no output and did not create a report file after ~25 min; it was stopped.
This review is therefore grounded directly in the UniProt record (Q9USQ5), the GOA
annotations, the PomBase API record, verified GO term definitions (QuickGO), and the
cached primary literature (PMID:10775274 full text; PMID:10871270 abstract). No
-deep-research-*.md file was fabricated.

Identity (verified — NOT the mammalian SPA1 GAP)

Provenance for function — this gene is directly, experimentally characterized

Despite being an understudied ORF, spa1 was functionally characterized in a dedicated primary
paper:

PMID:10775274 (Ivanov, Matsufuji, Murakami, Gesteland, Atkins, EMBO J 2000, "Conservation of
polyamine regulation by translational frameshifting from yeast to mammals"). Full text cached.
Key experimental results on the S. pombe gene itself (named "SPA" in the paper):

PMID:10871270 (Zhu, Karplus, Grate, Coffino, Bioinformatics 2000). HMM-based identification of
the S. pombe antizyme homolog; abstract-only cached. Establishes the sequence/family assignment
and the conserved frameshift signal
PMID:10871270.
Note: sequence identity to metazoan antizymes is low (~10% identity / ~24% similarity per
PMID:10775274; 18–22% in the most conserved C-terminal regions per PMID:10871270).

Mechanism by orthology (mammalian AZ1, UniProt Q02803)

UniProt propagates by similarity (ISS from Q02803 = rat AZ1): antizyme binds ODC monomers,
sterically blocking assembly of the active ODC homodimer, and targets ODC monomers for
ubiquitin-independent degradation by the 26S proteasome
[spa1-uniprot.txt lines 67–75 "Binds to ODC monomers, inhibiting the assembly of the functional ODC homodimer, and targets the monomers for ubiquitin-independent proteolytic destruction by the 26S proteasome"].
The Ivanov paper directly demonstrated ODC inhibition by SPA but did NOT test the
degradation-targeting or monomer-binding mechanism in S. pombe — that specific mechanistic step
is inferred from the mammalian ortholog, not shown for spa1.

Localization — KNOWN vs NOT known

Biological role and phenotypes (context; not GO-review targets)

Annotation-review plan

Term Aspect Ev Ref Planned action Rationale
GO:0008073 ornithine decarboxylase inhibitor activity MF IBA GO_REF:0000033 ACCEPT (core) Correct; also directly demonstrated in PMID:10775274
GO:0008073 ornithine decarboxylase inhibitor activity MF IEA GO_REF:0000002 (InterPro IPR002993) ACCEPT (core) Same term, domain-supported; redundant but correct
GO:1901305 negative regulation of spermidine biosynthetic process BP NAS GO_REF:0000051 KEEP_AS_NON_CORE (or MODIFY) Real (Δspa raises spermidine) but overly specific; broader "negative regulation of polyamine biosynthetic process" (GO:0170066, which UniProt/PomBase now use as TAS) better captures the function
GO:0005829 cytosol CC NAS GO_REF:0000051 KEEP_AS_NON_CORE Plausible but keyword-inferred, no experimental localization
GO:0005634 nucleus CC IBA GO_REF:0000033 MARK_AS_OVER_ANNOTATED / REMOVE Propagated from mammalian AZ nuclear shuttling; no evidence in S. pombe
GO:0005737 cytoplasm CC IBA GO_REF:0000033 KEEP_AS_NON_CORE Broad, consistent with cytosolic action; uninformative but not wrong

Note UniProt DR lines show PomBase now curates GO:0170066 negative regulation of polyamine
biosynthetic process (TAS) [spa1-uniprot.txt line 114], the more appropriate parent of the
GOA GO:1901305 spermidine-specific term.

Knowledge gaps (for the review)