Interpretations and Precautions regarding WIPO Standard 26 (ST.26)-the Standard for the Presentation of Nucleotide and Amino Acid Sequence Listings using XML

[ 2022-11-14 ]


Written by Dahao ZHANG (Mr.), Jirui ZHENG(Ms.) and Haoyu ZHOU (Elliot)


The China National Intellectual Property Administration (CNIPA) published a Notice on June 10, 2022, announcing that beginning from July 1, 2022, the electronic version of the sequence listings submitted to the CNIPA for both national applications and PCT international applications must comply with WIPO Standard ST.26. 

This is a big change to the ZC_0003-2001 Standard (Nucleotide and/or Amino Acid Sequence Listings and the Document Type Definition), which was issued by CNIPA 21 years ago with reference to the WIPO ST.25 Standard. In this article, we will discuss the details of the adjustment as well as other issues that may arise in practice.

1.  Which standard should be used, ST.25 or ST.26?

When filing patent applications in the biotech field, the applicant must first determine which format is acceptable by the receiving office. According to the CWS, the filing date determines the standard. For applications filed before July 1, 2022, the sequence listing must comply with Standard ST.25, whereas Standard ST.26 applies to all patent applications filed on or after July 1, 2022. However, some tricky situations may arise in special cases, which we will discuss separately below.

1.1 Patent applications without priority claim

All new applications (national, regional and international) filed on or after July 1, 2022 disclosing amino acid and nucleotide sequences must contain an ST.26 XML compliant sequence listing. Any sequence listing furnished in respect of any applications filed prior to that date should still follow WIPO Standard ST.25

1.2 Patent applications that claim priorities

For applications that claim priorities, there are two critical dates: filing date and priority date. As previously mentioned, the actual filing date should be referred to as the criterion for which standard will be used. Any patent applications filed on or before June 30, 2022 should continue to comply with Standard ST.25, while other applications filed on or after July 1, 2022 should comply with Standard ST.26. 

Extra caution should be taken with applications filed on or after July 1, 2022 but claiming an earlier priority prior to July 1, 2022. In this case, the sequence listings included in the prior application must be submitted in TXT format under Standard ST.25, and a transition from TXT to XML is required before filing the new applications. The WIPO Sequence Suite (a desktop tool developed by WIPO used to generate a ST.26-compliant sequence listing) may be used to assist the transition. Because the two formats are quite different, special cares should be taken to avoid any missing or addition of new content during the transition.

Furthermore, applications filed before July 1, 2022 should comply with WIPO Standard ST.25, even if sequence listing amendments are required on or after July 1, 2022. (For example, an applicant may amend his application on his own initiative or in response to OAs in accordance with Article 51 of the Detailed Rules for the Implementation of the Patent Law). For example, an application with a filing date of June 1, 2021 application included a sequence listing, and the applicant voluntarily modified the sequence listing on July 15, 2022. In that case, because the actual filing date was still prior to July 1, 2022, the modified sequence listing must still comply with the ST.25 Standard.

1.3 PCT applications entering the Chinese national phase

When an application enters the national phase via the PCT route, there are three official dates: priority dates, international filing dates, and national filing dates. The international filing date is the only criterion used to determine which standard should be used for the sequence listings. In this regard, for PCT applications with an international filing date prior to July 1, 2022, the applicant must submit a ST.25-compliant sequence listing; and the ST.26 Standard will apply to applications with an international filing date on or after July 1, 2022.

As the international phase typically takes longer than 18 months, it is common in practice that the international filing date was prior to July 1, 2022, while the national filing date is much later. In this case, ST.25 format sequence listings are still necessary even though the national filing date is much later than July 1, 2022. For example, if your international application was submitted on January 1, 2022, but you decide to enter the national phase on March 15, 2024, a date which is far later than July 1, 2022, you should still submit ST.25-format sequence listings to the designated Office.

Another issue that needs to be addressed is the modification of the sequence listings. If an applicant intends to modify the sequence listings provided in an application filed prior to July 1, 2022, the revised sequence listing must also comply with Standard ST.25. Such modifications usually occur in accordance with PCT Article 28/41 or Article 51 of the Detailed Rules for the Implementation of the Patent Law. For example, if an applicant filed an international application that disclosed DNA and RNA sequences but did not submit the electronic format of the sequence listing, when the applicant enters the national phase on, for example, July 20, 2023, in order to meet the requirement on the sequence listings of Designated offices, the applicant must generate a machine readable sequence listings that may have been disclosed in the drawing and submit to national/regional offices in accordance with the requirements on the sequence listings of Designated offices. In this case, even if the sequence listings are provided after July 1, 2022, the submitted sequence listings should be in ST.25 format because the international filing date was prior to July 1, 2022.

1.4 Divisional Applications

Despite the fact that divisional applications and parent applications have the same original filing date, the CNIPA has yet to make a decision on which standard should be followed when a divisional application is filed.

In response to this inquiry, WIPO states that this is a decision for the individual Patent Office to make, based on the national/regional law and other rules. Albeit the above, WIPO has suggested that if the divisional application's actual filing date is on or after July 1, 2022, the applicant is encouraged to submit ST.26-format sequence listings.

In view of the above, the format in which the sequence listing is filed should be decided on a case-by-case basis when dealing with new applications or amendments relating to sequence listings filed on or after July 1, 2022. It should also be noted that the aforementioned principles and provisions apply not only to Chinese national applications and WIPO international applications, but also to applications filed in a vast majority of contracting nations.

2 Consequence of Submitting the Non-compliant Sequence Listings

A frequently asked question is what if the sequence listings are found to be non-compliant later. While the CINPA has not issued a specific regulation, WIPO provide solutions for defects that may occur during the PCT international phase. 

2.1 For Cases where Sequence Listings are Submitted in ST.25 format rather than ST.26 format by Mistakes

If the ST.25 format is mistakenly filed in the PCT application, the applicant will be asked by WIPO to include the ST.25-format sequence listings into part of the specification, which will increase the page numbers and, of course, additional official fees. The deficiency can be addressed at the international phase by submitting a compliant ST.26 sequence listing as amendments under PCT Article 34, Article 28/41, or it can be remedied at the national phases under the respective national laws.

It should be noted that if the ST.25 sequence listings are incorrectly submitted, the applicant cannot submit the ST.26 sequence listings through a format amendment under PCT Rule 26.

In accordance with PCT Rule 20.5, the applicant could submit the ST.26 sequence listings as an omitted part, but the filing date will be re-determined as the date of submission of the ST.26 sequence listings.

Additionally, the applicant may request incorporation by reference based on the priority application, but this approach is not recommended due to the reservation of the Chinese Patent Law and some other jurisdictions on this regulation.

To sum up, the most recommended strategy to address the defect is to include the ST.25 sequence listing in the specifications and then submit ST.26-format sequence listings as amendment under PCT Article 34, Article 28/41 in the international phase or wait until the national stage to remedy such a deficiency to comply with the respective national patent laws.

2.2 What if the filed ST.26 Standard sequence listing contains a minor format issue?

       For general formal issues, the applicant may correct the defects under Rule 26 at the international stage, or the applicant may leave this matter to be addressed until the national phases. 


3. Precautions for Creating a ST.26-format Sequence Listing

Extra attention need to be paid to issues that may arise during the creation or transition of a sequence listing in ST.26 format.

For applications filed on or after July 1, 2022, based on either the Paris Convention or the PCT route, they normally claim priority from applications with a WIPO Standard ST.25 sequence listing. For these cases, the applicant should use WIPO Sequence Suite to convert the ST.25 sequence listing to WIPO ST.26 format. Due to the differences between Standard ST.26 and ST.25, we must pay special attention to the following points.

3.1 Short Sequences

        One of the significant changes of ST.26 is that the sequence listing must not include any sequences having fewer than ten specifically defined nucleotides, or fewer than four specifically defined amino acids. That means the above short sequence, which was originally recorded in the ST.25 TXT format, will not be reflected in ST.26 format sequence listings. To prevent the risk of missing any short sequences in the sequence listing, it is advisable to the applicant that such short sequences are included in the specification.


3.2 Feature Keys

ST.26 Standard indicates that every sequence should include mandatory feature keys, i.e., “source”, and every “source” should include two mandatory qualifiers “mol_type” and “organism”, which may not be required in the ST.25 compliant sequence listings. In particular, for the qualifier "mol_type" under the “source" of nucleotide molecules, which includes "genomic DNA", "other DNA", and "unassigned DNA", these expressions are not available in the ST.25 sequence listings. For example, it is acceptable in the ST.25 Standard that only a biological origin (e.g., Escherichia coli) of a DNA molecule is stated, without the necessity of describing whether it is a genomic DNA; but for ST.26 Standard, it is necessary to describe the "mol_type" (molecular type) of the DNA molecule, that is, to select the appropriate type from the three mentioned types to avoid introducing new content. 

The qualifier-value of the "mol_type" needs to be determined according to the technical solution of the application and then fill in the sequence list by the WIPO Sequence Suite. It should be noted that incorrectly filling in this qualifier value may possibly result in an introduction of new matter compared to the priority document or description, so the attorneys should make correct decision and ask for opinions form the applicant/inventor when there is any uncertainty.

In addition, due to the difference in the format between the ST.25 Standard and the ST.26 Standard, additional cautions should be made at the time of doing the transitions, and try to avoid any new matters. For other questions, please refer to Part VII of the official ST.26 Standard.

3.3 Text and Translation of Sequence Listings

For non-Chinese language applications (e.g., new applications based on the Paris Convention or PCT applications entering into Chinese national phase), the WIPO Sequence Suite can be used for translation. According to ST.26 Standard, there are special elements that must be formatted in English and cannot be translated into other languages, such as the feature key "source", the qualifier "mol_type", etc. For the ST.26-format sequence listings, there are normally two parts that need to be translated into official languages.

One is the basic information, which includes the applicant’s name and the title of the invention. For the applicant’s name, it is required to file in both English and Chinese according to the Chinese Patent Law.

The other one is the free text part of the language-dependent qualifier, for which section, the WIPO Sequence Suite provides additional columns for applicants to fill in other languages, including Chinese. Furthermore, according to WIPO Sequence Suite, the applicant can export text in bulk and then import the translated text back into the sequence listings in the same way. 

However, the current version of the WIPO Sequence Suite contains bugs, such as inconsistencies between the priority date in PDF files generated by the print application and the priority date in sequence listings in the XML format.  We are looking forward to further improvement of the software.

The implementation of the new Standard will increase the workload on sequence-based patent applications in the near future, particularly with regard to the transition of sequence listings, and this is almost inevitable within the next year. However, in the long run, since all the member states agreed to follow WIPO Standard ST.26 in XML format, which may likely reduce the office actions received caused by inconsistencies in the formats of sequence listings required by different offices, so it would be suggested that under ST.26 Standard, one sequence listing could be filed to all jurisdictions without much additional adaptive modifications. 


1.Fifty-Fourth (25th Ordinary) Session of WIPO General Assembly

2.Standard – ST.26,90,316

3.WIPO Standard ST.26 FAQs

4.Announcement on Adjustment of Electronic Document Standards for Nucleotide or Amino Acid Sequence Listings (No. 485)

5.WIPO Sequence Suite