What symbols are used for amino acids in a sequence listing?

This page is an FAQ based on guidance from the Manual of Patent Examining Procedure. It is provided as guidance, with links to the ground truth sources. This is information only: it is not legal advice.

In a sequence listing, amino acids are represented using specific symbols as defined by WIPO Standard ST.25. According to MPEP 2423.01:

“The amino acids in a protein or peptide sequence must be represented using the three-letter abbreviation with the first letter as a capital.”

Here are some key points about amino acid symbols in sequence listings:

• Use three-letter abbreviations (e.g., Ala for Alanine, Lys for Lysine)
• The first letter of each abbreviation must be capitalized
• Unknown or modified amino acids are represented by “Xaa”
• Termination codons are represented by “***”

It’s important to use these standardized symbols to ensure clarity and consistency in sequence listings across patent applications.