How should unknown amino acids be represented in a sequence listing?

The MPEP 2412.05(d) provides guidance on representing unknown amino acids in sequence listings:

• Use the symbol ‘X’ to represent unknown amino acids
• Provide further description in a feature table
• Use the feature key “UNSURE” and optionally the qualifier “note”

The MPEP states, “Any “unknown” amino acid must be represented by the symbol “X” in the sequence. An “unknown” amino acid designated as “X” must be further described in a feature table (see MPEP § 2413.01(g), subsection I, for more detail regarding a “feature table”) using the feature key “UNSURE” and optionally the qualifier “note.” The symbol “X” is the equivalent of only one residue (WIPO Standard ST.26, paragraph 32).” This approach ensures clarity and consistency in representing unknown amino acids across patent applications.

To learn more:

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