SEPTIN14P20 (C0HM01, RBRP) review notes

2026-10-08 - MICROPROTEINS Tier 2 review (claude-code)

Identity / existence. 71-aa "putative RNA-binding regulatory peptide". UniProt PE5
(Uncertain) with CAUTION "Could be the product of a pseudogene". HGNC: pseudogene
(septin 14 pseudogene 20; prev. symbols LINC00266-1, C20orf69, NCRNA00266). 20q13.33.
It has its own HGNC symbol, so the standard folder convention applies.

Bioinformatics (SEPTIN14P20-bioinformatics/RESULTS.md): RBRP 1-47 is 47/47 identical to
SEPTIN14 383-429; only residues 48-71 are unique. The IGF2BP1-binding residue Gly-19 is septin
sequence (SEPTIN14 Gly-401). This contradicts the paper's statement
PMID:32245947
The endogenous MS used a custom database
PMID:32245947
so SEPTIN14-shared peptides cannot be excluded; the antibody epitope (TDTKKDKHPDPY) is
8/12 SEPTIN14-shared.

Literature. PubMed search for RBRP / LINC00266-1 / SEPTIN14P20 finds only PMID:32245947
(functional) and PMID:32709857 (LINC00266-1 as a ceRNA lncRNA in osteosarcoma; RNA-level,
not about the peptide; not cited in the review). One-paper peptide.

Key claims, PMID:32245947 (full text, PMC7125119):
- RNase-resistant IGF2BP1 binding via KH3-4; G19A abolishes it.
- Recombinant RBRP increases recombinant IGF2BP1 binding to m6A RNA
PMID:32245947
- MYC mRNA stabilisation, IGF2BP1/METTL14/m6A-site dependent; rescue by WT but not G19A
PMID:32245947

Decisions. 3 rows. protein binding (IPI, IGF2BP1) -> MODIFY to GO:0140677 molecular
function activator activity (supported by recombinant in vitro data). mRNA stabilization and
positive regulation of mRNA binding (IDA) -> ACCEPT: locus-specific, full-text experimental
evidence, so the Tier 3 doubtful-existence rule (aimed at inherited rows) does not force
removal; caveats (PE5, pseudogene, single lab, SEPTIN14 identity) recorded on the reference
(DISPUTED) and a finding_review. No NEW terms.