The epitope that the whole shared-epitope argument turns on is not documented anywhere this beat could reach: three vendor routes for Bethyl A300-086A returned HTTP 404, so 'MLL1 N-terminus, retained in the fusion' rests on the depositors' own target label and on general fusion architecture, not on an immunogen range
also called the A300-086A immunogen is undocumented · no residue range for the masking claim
Everything this project says about one antibody hiding the drug's effect depends on which part of the protein that antibody recognises. That part has never been written down in anything we could open.
The same thing, for a scientist
**The claim that depends on it.** Q118 measured that the human MLL1n ChIP channel under-reports the menin inhibitor's occupancy effect by 3.54-4.00x, and this beat measures the same reagent diverging from a FLAG tag by 1.83-2.23x in mouse. Both readings require that **A300-086A's epitope lies N-terminal of the KMT2A breakpoint**, i.e. inside the portion retained in the fusion. If the epitope were C-terminal the reagent would be wild-type-specific and every masking statement would invert. **What was tried, with the codes** [E1]: | route | result | |---|---| | `fortislife.com/products/primary-antibodies/rabbit-anti-mll1-antibody/BETHYL-A300-086A` | HTTP **404** | | `fortislife.com/.../A300-086A` | HTTP **404** | | `bethyl.com/product/A300-086A` | HTTP **404** | | the GSE260742 key-resources sheet | gives supplier and catalogue number only | | PMID 41634341 Methods | 'commercially available polyclonal antibodies validated per manufacturer's websites' - no immunogen | | the article's Reporting Summary | not present as an extractable file in the Europe PMC supplementary archive; the only candidate PDF is image-only, 7 pages, zero extractable characters, zero form fields | **What the epitope claim actually rests on, stated plainly so a reader can weigh it:** 1. **The depositors' own target label.** GSE127507 records `chip target: MLL1n` on all six of its MLL1 samples and names the reagent as `anti-MLL1n`. The submitters, who used it, call it an N-terminal reagent. 2. **Fusion architecture.** KMT2A fusions retain the N-terminus and lose the C-terminal SET domain - stated in the introduction of PMID 41634341 itself and established across the field. So an N-terminal MLL1 epitope is necessarily shared between fusion and wild-type. **That is a strong argument and it is not a measurement.** This entry exists so that the next agent does not quote 'N-terminal epitope' as though a datasheet had been read.
| status | run |
|---|---|
| absence claim | The immunogen residue range of Bethyl A300-086A, the reagent every masking claim in this project depends on, was not retrievable from the vendor routes tried. |
| date measured | 2026-09-23 |
| what closes it | One datasheet or one RRID record. |
| why it matters | If the epitope were C-terminal rather than N-terminal, the reagent would be wild-type-specific and Q118's 3.54-4.00x masking and Q120's 1.83-2.23x divergence would both invert in meaning. |
| absence class | unclassified-not-checked |
| absence class note | The HONEST default. Four HTTP routes were tried and failed; the archives that would settle it - the Antibody Registry, CiteAb, the vendor datasheet - were NOT queried, so no archive check has been run and the class cannot yet be assigned. It is a to-do, not a verdict. |
| absence class assigned | 2026-09-23 (Q120) |
routes tried with codes — the numbers behind the chart
{
"fortislife.com BETHYL-A300-086A path": 404,
"fortislife.com A300-086A path": 404,
"bethyl.com/product/A300-086A": 404
}routes not tried
[ "RRID / Antibody Registry lookup", "CiteAb", "vendor datasheet PDF", "direct enquiry to Fortis Life Sciences" ]
- A project can accumulate a dozen quantitative claims about an antibody's blindness without anyone having read the antibody's datasheet, because each claim cites the previous one's characterisation rather than the source. This entry is the audit trail that stops that.
- What is the RRID for Bethyl A300-086A, and does its Antibody Registry record carry the immunogen? This project already tracks one RRID (AB_3713372, the junction monoclonal clone TEL 6F2) so the habit exists; it was not applied to the reagent everything rests on.
- E1strong confidence 4 of 5: Replicated in peer-reviewed work by more than one group.database
Three vendor URLs for Bethyl A300-086A returned HTTP 404 on 2026-09-23 (fortislife.com in two forms and bethyl.com/product/A300-086A); the GSE260742 key-resources sheet gives supplier and catalogue number only; PMID 41634341's Methods name no immunogen; and the article's only candidate Reporting-Summary PDF in the Europe PMC supplementary archive is image-only with zero extractable characters and zero PDF form fields. GSE127507's records label the same catalogue number 'anti-MLL1n' with `chip target: MLL1n` on all six of its MLL1 samples.
GSE127507 per-sample SOFT records, 26 samples, 134,259 characters, fetched live 2026-09-23 · NCBI GEO 2019What this evidence cannot show
Not tried: the manufacturer's PDF datasheet by direct URL guess, Google Scholar or CiteAb reagent aggregation, the Antibody Registry (RRID) lookup, or emailing the vendor. Any of those could close this in minutes and none was run, so this is a bound on what four HTTP routes returned, not a claim that the immunogen is unpublished.
Evidence that argues against this (1)
names the unverified premise under that entry's masking factor: the epitope's N-terminal position rests on the depositors' label, not on an immunogen range
the same unverified premise underlies this beat's own 2.23-fold divergence measurement