ST.25 vs ST.26: A Comparative Analysis of Patent Sequence Listing Standards  

The world of intellectual property is vast and complex. Various standards and guidelines ensure to document these inventions and innovations correctly. Specifically, in the realm of biotechnology and genetic engineering, patent sequence listings play a crucial role in applications as they provide a detailed representation of the nucleotide and amino acid sequences that make up an invention. Over the years, several standards have been established to govern the formatting and submission of these patent sequence listings. Notably, two of the most significant patent sequence listing standards in this area are ST.25 and ST.26.

In this article, we will delve into the differences between these two standards, exploring their respective strengths and weaknesses for patent sequence listing preparation. 

ST.25: The Traditional Standard for Patent Sequence Listing  

The ST.25 standard, which was established by the World Intellectual Property Organization (WIPO) in 1998, is a crucial guideline for patent sequence listings in biotechnology and genetic engineering. It outlines the format and necessities for textual representation of nucleotide and amino acid sequences and their associated annotations. ST.25 requires that sequence listings be submitted as American Standard Code for Information Interchange (ASCII) text files, which are both human-readable and machine-readable.

However, ST.25 also has its drawbacks: 

  • Limited functionality: The ASCII text format limits the complexity and functionality of sequence listings. For instance, it does not support the inclusion of graphical information or advanced annotations. 
  • Size constraints: Large sequence listings can result in unwieldy text files that are difficult to handle and process. 
  • Inconsistency: The potential for human error in creating ASCII text listings can introduce inconsistencies. As a result, it can lead to errors in sequence representation. 

ST.26: A Modern Approach for Patent Sequence Listing 

Recognizing the limitations of ST.25, the WIPO implemented the new standard for patent sequence listing, ST.26, in 2022. ST.26 addresses the shortcomings of ST.25 while maintaining compatibility with existing systems, and it is based on eXtensible Markup Language (XML). Key benefits of ST.26 include the following: 

  • Enhanced functionality: XML allows for richer data representation and the inclusion of additional annotations, providing a more comprehensive picture of the invention. 
  • Graphical support: ST.26 supports the inclusion of graphical representations, enabling a better understanding of complex sequence relationships. 
  • Reduced file size: XML format enables more efficient data storage and smaller file sizes, simplifying the handling and processing of sequence listings. 
  • Consistency: XML data can more easily undergo validation against established rules and schemas, making it less prone to human error and therefore, ST.26 is beneficial in this regard.

Also Read:- The Art of ST26 Sequence Listing Preparation: Best Practices For Accuracy and Compliance

Difference Between ST.25 and ST.26 Sequence Listing Standards 

The table below lists the major differences between ST.25 and ST.26. It also emphasizes how the ST.26 standard has simplified the application for patent sequence listing. 

Category ST.25 Standard ST.26 Standard 
Formatting Numerical identifier formatted ASCII text. XML format containing components and attributes that use UTF-8 (Unicode) encoding. 
Sequences allowed Not necessary to mention: D-amino acids  Linear sections of branched sequences  Nucleotide analogs Must have:   D-amino acids  Linear sections of branched sequences Nucleotide analogs 
Sequence annotation Only feature keys Key features as well as qualifiers 
Acceptable sequences Sequences can include: Less than 10 specifically defined nucleotides Less than 4 specifically defined amino acids Unacceptable sequences: Less than 10 specifically defined nucleotides Less than 4 specifically defined amino acids Note: Any nucleotide and amino acid other than “n” and “X” is regarded as being “specifically specified.” 
Priority applications Possible to incorporate all priority applications. Only the most important application can be submitted. 
Applicant and inventor names The names of all applicants and inventors may be listed. There can only be one applicant name and potentially one inventor name. These should be the first/primary applicant or innovator. 
Invention titles Only one invention title can be mentioned. It is possible to include several invention titles in different languages. 
Character usage Normal Latin characters must be used to write the inventors’ names and the names of their inventions. Invention titles can contain any valid Unicode character, and inventor names can contain any valid Unicode character combined with a basic Latin translation. 
Sequence categorization Sequences are only categorized as DNA, RNA, or PRT. Sequences are classified as DNA, RNA, or AA and as the mandatory qualifier “mol type” to further specify the type of molecule. 
Organism names Organism names:  Latin genus/species Virus name “Artificial sequence”  “Unknown” Organism names:  Latin genus/species Virus name “Synthetic construct” “Unidentified” 
Nucleotide symbols “u” stands for uracil in nucleotide sequences. The symbol “u” is not a recognized nucleotide symbol. In DNA and RNA sequences, the letter “t” stands for thymine and uracil, respectively. Modified nucleotide bases uracil in DNA and thymine in RNA must be represented by the symbol “t” in ST.26, and described in a feature table using the feature key “modified base.” 
Amino acid symbols Three-letter acronyms are used to represent amino acid sequences. One-letter acronym is used to represent an amino acid sequence. 
Variable residues The definition of “n” and “Xaa” variable residues must be provided in a feature. A default value is assumed for “n” and “X” variable residues with no definitions. A definition is essential when “n” or “X” represent residues other than the default value. 
Feature location The format for feature locations is not clearly defined. Strictly defined formats for feature location; allows usage of “<” and “>” in all sequence types as well as “^,” “join,” “order,” and “complement” in nucleotide sequences. 

Table: Key Differences between ST.25 and ST.26 Standards 

As demonstrated in the above table, ST.26 brings about several improvements over ST.25 patent sequence listing standard. Specifically, the new standard adopts a more structured and consistent approach to data representation. As a result, it becomes easier for patent examiners to understand the invention and ensure that it meets the criteria for patentability.

Additionally, ST.26 includes a range of new features that make it easier for patent applicants to submit their patent sequence listings, such as the ability to use compressed files. However, the new standard also requires patent applicants to provide additional information, which may be sensitive or proprietary, increasing the risk of unauthorized disclosure. Furthermore, it requires more extensive formatting of sequence listings, which can be time-consuming and challenging for patent applicants. 


While ST.26 brings about several significant improvements over ST.25, patent applicants must be aware of the potential drawbacks and ensure that they adhere to the new standard’s requirements while protecting their sensitive information. ST.26 offers a more modern approach with enhanced features and capabilities, addressing many of the limitations associated with the older standard. With proper understanding and adherence to the updated Sequence Listing Standard, patent applicants can increase their chances of successfully protecting their inventions. 

However, the WIPO may decline your patent sequence listing application if you do not adhere to their sequence listing standards. At TSLC, our team of patent specialists can assist you in creating accurate sequence listings that conform to the latest regulations. Check out our sequence listing service page for more information. 

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