30 November 2022

Standard ST.26 (ST.26) changes and the Big Bang

Although the “Big Bang” might be considered to relate to the start of the universe for many, this is not the case for patent attorneys and those at the World Intellectual Property Organisation (WIPO). Instead, this relates to 1 July 2022, the date on which the new WIPO standards for sequence listings came into force.
These changes have been anticipated for some time and are intended to bring about improvements, clarity, and uniformity to sequence listings. Here, we will cover some of the changes and key factors to be aware of.

What is ST.26?

ST.26 is the new sequence listing requirement set by WIPO, replacing the previous requirement, Standard ST.25 (ST.25), which was adopted in 2009. The requirement sets the standard for the presentation of nucleotide and amino acid sequence listings in patent applications and must be followed in order to avoid potential formality and added matter objections.

All new applications, including priority and priority claiming applications, must use ST.26 compliant sequence listings if a sequence listing is to be filed. However, use of

ST.26 in divisional applications is a matter of national law (most Intellectual Property offices will require ST.26 compliant sequence listings) as we discuss further below.

ST.26 is a more thorough and complex set of requirements than ST.25, and so transferring data between the two formats will require manual intervention.

Brief summary of changes

The new sequence format is an XML file format and provides more information about each sequence, such as the type of molecule for nucleic acid sequences.
The criteria for a sequence to be included in a listing has changed. There is a new minimum sequence length of ten specifically defined nucleotides or four specifically defined amino acids, and shorter sequences must not be included in the listing. The definitions of amino acids and nucleotides have been expanded, meaning that more sequence types are now covered, and “u” is no longer used as a symbol, so that uracil in RNA is represented by “t” rather than “u.”

Insertions and substitutions have been clarified, for example, they can be included as feature annotations of a sequence provided that they are independent of each other. If any insertion or substitution sequences themselves meet the minimum sequence length criteria, they should additionally be listed as their own separate sequences with their own sequence ID.

ST.26 has a new feature known as the “mol_type,” in which the sub-type of the molecule is denoted. Options in this field include “genomic DNA,” “mRNA,” and “tRNA,” among others, but non-naturally occurring sequences (synthetic constructs) must be indicated as “other RNA” or “other DNA” and naturally occurring in vivo sequences of unknown subtype should be indicated as “unassigned RNA” or “unassigned DNA.”

“Mixed mode” sequences, which include the nucleotide and accompanying protein sequence, are no longer possible, but instead nucleotide sequences can be listed to include the feature “CDS” which can identify coding sequences and be qualified with the “translation.” The protein sequence itself however should be given its own ID. Amino acids are now represented by a single capital letter rather than three-letter codes.

Finally, bibliographic data is limited to one applicant, optionally one inventor, and details of the earliest priority application only.

How is the change being dealt with in different territories?

The UK Intellectual Property Office (UKIPO) has taken a relatively relaxed approach to the change. For example, divisional applications for which the parent application comprises an ST.25 listing may also use ST.25 listings after 1 July 2022.

If the application includes a non-compliant sequence listing, then after identification during preliminary examination the applicant will have 15 months from the filing date to provide a compliant sequence listing, and this will not delay publication.

In contrast to the UKIPO, the European Patent Office (EPO) requires that such divisional applications must have ST.26 compliant listings, as must applications filed by reference to earlier applications.

Likewise, the United States Patent and Trademark Office has announced that the ST.26 standard will be required for continuing and divisional applications, and ST.26 is required for any application with a filing date on or later than 1 July 2022, regardless of an earlier priority claim.

All new international (PCT) applications including biological sequence listings must include the sequence listing in the ST.26 file format from 1 July 2022. However, for PCT applications filed before 1 July 2022 but entering the national or regional phase after 1 July 2022, the ST.25 standard still applies.

Added matter

With the EPO’s requirement that divisional applications require ST.26 compliant listings regardless of the format of the parent application’s listing, parent application sequence listings in ST.25 format may need to be changed into ST.26 format for the divisional application. This could generate issues due to the EPO’s strict requirement that a divisional application does not add matter over the disclosure of the parent application. As noted above, ST.26 requires more information than ST.25 listings so addition of this information could extend the subject-matter beyond that originally disclosed in the parent application. Added matter might also be a concern when there is a lack of clarity in the earlier ST.25 sequence listing, and this lack of clarity is addressed by the ST.26 listing.

The EPO has advised that potential added matter problems can be avoided by adding the parent ST.25 sequence listing to the description of the divisional application when it is filed, and then subsequently filing the ST.26 sequence listing for search purposes only, rather than as part of the description. However, an additional fee may fall due if the required ST.26 sequence listing is filed after the divisional application filing date, and excess page fees may increase if the ST.25 listing of the parent is added to the description. Neither is ideal for the applicant.

Preparing ST.26 Sequence Listings

Although the new XML file format is user-friendly and applicants may use any XML-editing tool, it is recommended to use the WIPO Sequence desktop tool, which has been designed to handle the complicated data associated with the new ST.26 requirements. Sequences may be validated using the same tool, but WIPO Sequence Validator, a web service, has been designed for patent offices to check the compliance of filed sequence listings with the ST.26 standard.


The new ST.26 standard introduces a multitude of new requirements and changes. Though the new WIPO sequence application is helpful for navigating these changes, care must be taken with the new features, especially when converting an ST.25 compliant listing to be ST.26 compliant. This is particularly true when preparing sequence listings for divisional applications, due to the potential added matter issues highlighted above.