What symbols should be used to represent amino acid sequences?

According to WIPO Standard ST.26, amino acids in a sequence must be represented using the one-letter codes specified in Table 3: List of Amino Acids Symbols. Key points include:

• Only uppercase letters must be used.
• Each symbol represents only one residue.
• Use the most restrictive symbol for ambiguities (e.g., “B” for Asp or Asn, not “X”).
• “X” represents any amino acid, unless further described in the feature table.

The MPEP states: “Any symbol used to represent an amino acid is the equivalent of only one residue.“

To learn more:

• amino acid sequences
• WIPO Standard ST.26
• sequence symbols