New “Sequence Listing” Standard

New “Sequence Listing…

As of July 1, 2022, Intellectual Property Offices will be enforcing the World Intellectual Property Organization (WIPO) Standard ST.26, which prescribes requirements for the presentation of nucleotide and amino acid sequence listings in patent applications.

Standard ST.26 (“ST.26”), which replaced ST.25, is intended to establish a single format for sequence listings that is acceptable worldwide and is compatible with international databases. The full text of ST.26 can be found here.

USPTO PowerPoint slides providing an overview of ST.26 can be found here.

What about Continuing Applications?

Any sequence listing submitted in a Continuing or Divisional Application having a filing date on or after July 1, 2022 must comply with ST.26 format, even if the parent application has a filing date on or before June 30, 2022.

XML Format

Under ST.26, sequence listings must be presented as a single file in XML, rather than the “plain text” TXT format used under ST.25.

WIPO Sequence Software

XML editing software must be used to prepare sequence listings that comply with ST.26.

WIPO has developed its own software, called WIPO Sequence (which can be downloaded here), which is designed to create and edit ST.26 compliant sequence listings. The software includes a validation tool which generates a verification report identifying potential errors.

In addition, ST.25 compliant sequence listings in TXT can be converted to XML using WIPO Sequence. Annex VII of ST.26 sets out recommendations for the transformation of a sequence listing from ST.25 to ST.26.

ST.26 Changes the Minimum Length Requirement for Sequence Listings

Sequence listings are limited to unbranched sequences and linear regions of a branched sequences containing (i) 10 or more specifically defined nucleotides; or (ii) 4 or more specifically defined amino acids.

ST.26 specifically prohibits the inclusion of sequences which are shorter than the minimum, whereas ST.25 did not.

Only “specifically defined” residues count toward the length, and the term “specifically defined” means any nucleotide other than those represented by the symbol “n” and any amino acid other than those represented by the symbol “X”.

For example, a nucleotide sequence represented by 5’-acgtnnacgt-3’ has only eight specifically defined nucleotides and, therefore, is prohibited from being included in a sequence listing.

Annex VI of ST.26 provides a guidance document with illustrated examples which serve to further clarify the above-noted criteria.


While XML documents look very different from TXT documents, the new WIPO Sequence software permits applicants to prepare compliant sequence listings and view a more understandable version of the sequence listing.

If you have questions or would like more information regarding the new ST.26 standard, we would be happy to speak with you.

Categories: Patents