How are modified amino acids represented in a sequence listing?

According to MPEP 2412.05(d), modified amino acids should be represented as follows:

• Represent as the corresponding unmodified amino acid when possible
• Use ‘X’ for modified amino acids that cannot be represented by other symbols
• Provide further description in a feature table

The MPEP states, “WIPO Standard ST.26, paragraph 29, specifies that modified amino acids, including D-amino acids, should be represented in the sequence as the corresponding unmodified amino acids whenever possible. Any modified amino acid in a sequence that cannot otherwise be represented by any other symbol in Table 3: List of Amino Acids Symbols (reproduced in MPEP § 2412.03(a)), i.e., an “other” amino acid, must be represented by “X”.” Additionally, modified amino acids must be further described in a feature table using appropriate feature keys and qualifiers.

To learn more:

• modified amino acids
• sequence listing
• WIPO Standard ST.26
• feature table