Sequence Listing Requirements in European Divisional Patent Applications

For biotech, pharma and life sciences applicants, filing a divisional application at the European Patent Office involves an extra layer of complexity that most other technology fields never encounter: the sequence listing. Since the 2022 transition to WIPO Standard ST.26, sequence listings for divisionals have become a genuine trap for the unwary  – capable of triggering added-matter objections, late fees and excess page charges if handled carelessly. This guide explains the current rules, where the risk lies and how to file a divisional cleanly.

1. What a Sequence Listing Is and Why It Matters

A sequence listing is a standardized, machine-readable disclosure of nucleotide and/or amino acid sequences referenced in a patent application  – required under Rule 30 EPC whenever an application discloses a qualifying biological sequence. Practically, it typically covers:

• Nucleotide sequences of a defined minimum length
• Amino acid sequences of a defined minimum length
• Associated organism, feature and annotation data identifying what each sequence is and does

Because the sequence listing forms part of the technical disclosure, it’s subject to the same added-matter rules as the rest of the application: nothing in the listing (or removed from it) can introduce or drop subject matter relative to what was originally filed.

2. The ST.25-to-ST.26 Transition

Historically, sequence listings followed WIPO Standard ST.25  – a text-based format. As of 1 July 2022, the EPO (along with most major patent offices worldwide) requires new applications to use WIPO Standard ST.26, an XML-based format with materially different and more detailed data requirements than ST.25, including more granular feature annotation and organism metadata.

Two dating rules matter here:

• The relevant date is the actual filing date, not the priority date. An application claiming priority from a 2019 filing but filed at the EPO in 2026 still needs an ST.26 listing.
• For PCT applications, the relevant date is the international filing date. A PCT application filed before 1 July 2022 that enters the European regional phase after that date is still governed by ST.25 for its European phase, since the underlying international filing date controls.

Because ST.26 requires more structured data than ST.25, converting an older ST.25 listing into ST.26 format is not a mechanical exercise  – it requires judgment calls about annotation and categorization that can inadvertently add or lose subject matter relative to the original disclosure. This conversion risk is exactly where divisional applications become a pressure point.

3. Why Divisionals Are a Special Case

A divisional application is legally treated as an independent European application for procedural purposes, even though it’s entitled to the same filing date as its parent under Article 76(1) EPC. The EPO’s position has been that this independence extends to sequence listing format: a divisional application filed on or after 1 July 2022 must comply with ST.26, even if its parent was filed  – and disclosed its sequences  – under ST.25.

This creates a genuine conflict:

• Article 76(1) EPC requires that a divisional not add matter beyond what the parent disclosed and that it be treated as if filed on the parent’s original filing date.
• But converting an ST.25 sequence listing to ST.26 format inherently risks introducing new characterizations, annotations, or categorizations that weren’t in the original ST.25 disclosure  – creating exactly the kind of added-matter risk Article 76(1) is designed to prevent.

Professional representative bodies (notably epi, the Institute of Professional Representatives before the EPO) pushed back hard on this policy after the July 2022 transition, arguing it created unnecessary risk and burden  – particularly for divisionals with large, complex sequence listings that face a tight filing deadline and can’t easily absorb a lengthy, risk-laden manual conversion process.

4. The EPO’s Guidance for Avoiding Added Matter

In response to this pressure, the EPO laid out (and later refined) a practical route for applicants to file a divisional without taking on unnecessary added-matter risk:

Option A  – File without a new ST.26 listing at filing, then supply it afterward. Under this approach, the divisional is filed on the filing date without an ST.26 sequence listing forming part of the application as filed. Instead:

• The original ST.25 sequence listing from the parent is added into the description of the divisional (or the divisional is filed by reference to the parent’s description) to preserve the exact original disclosure and avoid added matter.
• The ST.26-compliant sequence listing is then filed separately, after the filing date, under Rule 30(3) EPC  – typically for search purposes, once the EPO invites it (or proactively, to avoid a late fee  – see below).

Because a sequence listing filed this way does not form part of the application as originally filed, it cannot itself add matter to the application. This is the core of the EPO’s advice and it remains the standard recommended route for divisionals bridging the ST.25/ST.26 transition.

Option B  – File a PDF-format ST.25 listing as a “safeguard.” Applicants can include the original ST.25 listing as a PDF annex or as text within the description at filing, preserving the exact original wording and then furnish the properly formatted ST.26 XML listing afterward under Rule 30(3) EPC.

Both routes avoid added matter by keeping the original ST.25 content intact as filed and treating the ST.26 conversion as a separate, subsequent, non-substantive filing step.

5. Fees: What Changed in November 2023

The practical downside of the EPO’s original advice was cost. Filing a lengthy ST.25 listing within the description (rather than as a properly formatted sequence listing) meant it counted toward the application’s page count  – and sequence listings can run to hundreds of pages, triggering significant excess page fees. Separately, furnishing the ST.26 listing after filing under Rule 30(3) EPC could trigger a late furnishing fee.

Following continued pressure from epi and applicants, the EPO announced a policy change, effective from its 30 November 2023 Official Journal notice:

• No excess page fees apply where an ST.25 sequence listing is added to the description of a divisional application as a safeguard against added matter.
• No excess page fees apply where the divisional is filed by reference to the parent application and an ST.25 sequence listing is contained in the certified copy furnished under Rule 40(3) EPC.

This substantially reduced the financial penalty for using the EPO’s recommended added-matter-avoidance strategy. The late furnishing fee for the ST.26 listing itself under Rule 30(3) EPC can still apply, but applicants can avoid it by proactively filing the ST.26 listing before the EPO issues an invitation to do so, rather than waiting to be prompted.

6. Practical Filing Checklist for Divisionals with Sequence Listings

1. Determine the parent’s original sequence listing format. If the parent predates 1 July 2022, it was very likely filed in ST.25 format  – confirm this before assuming any conversion path.
2. Preserve the original ST.25 disclosure at filing. Either incorporate the ST.25 listing into the divisional’s description, or file the divisional by reference to the parent’s description (relying on the certified copy under Rule 40(3) EPC), to lock in the original disclosure and avoid added-matter risk from format conversion.
3. Do not file a converted ST.26 listing as part of the application as filed unless the conversion has been carefully checked against the original ST.25 content for consistency  – doing this at filing creates real added-matter exposure if anything shifts in the conversion.
4. File the ST.26-compliant listing separately, proactively, under Rule 30(3) EPC, ideally before the EPO’s invitation, to avoid the late furnishing fee.
5. Use WIPO’s free validation tooling (the WIPO Sequence software) to check the converted ST.26 XML file for format compliance and internal consistency before submission  – this catches structural errors before the EPO does.
6. Cross-check every sequence referenced in the claims and description against the listing. Examiners actively compare the specification to the sequence listing and any mismatch  – a sequence cited in the claims but missing or altered in the listing  – triggers a formal objection under Rule 30 EPC.
7. Don’t assume the parent’s listing “carries over” automatically. Each divisional is procedurally independent and needs its own compliant sequence listing furnished in the correct format, even where the underlying biological content is identical to the parent’s.
8. Watch your filing timing. Because these rules and their fee treatment have shifted materially since 2022, confirm current EPO practice (via the latest Official Journal notices and the EPO’s sequence listing guidance pages) before filing, particularly if your divisional has a large or complex listing where the stakes of getting this wrong are highest.
9. Compare jurisdictions if filing in parallel. Practice is not uniform: some offices (for example, the UK IPO in certain circumstances) have taken a more permissive approach to carrying over an ST.25 listing for divisionals without requiring conversion, in contrast to the EPO’s stricter position. Don’t assume EPO practice applies elsewhere.

7. Way Forward

The EPO’s insistence that divisional applications comply with ST.26  – regardless of the format used by the parent  – creates a real tension between the no-added-matter requirement of Article 76(1) EPC and the mechanics of converting a legacy ST.25 sequence listing. The EPO’s recommended workaround (preserve the original ST.25 content at filing; furnish the ST.26 listing separately under Rule 30(3) EPC) resolves the added-matter risk and the November 2023 fee waiver removed much of the cost penalty that made the workaround unattractive. For biotech and life sciences applicants, the practical lesson is to treat sequence listing strategy as a planning item from the moment a divisional is contemplated  – not a formality to be resolved the week before the filing deadline..