Source: World Intellectual Property Organization (WIPO) Handbook on Industrial Property Information and Documentation, Standard ST.25: Standard for the Presentation of Nucleotide and Amino Acid Sequence Listings in Patent Applications (2009).
| Symbol
| Meaning
| Origin of designation
|
|---|
| a | a | adenine.
|
| g | g | guanine.
|
| c | c | cytosine.
|
| t | t | thymine.
|
| u | u | uracil.
|
| r | g or a | purine.
|
| y | t/u or c | pyrimidine.
|
| m | a or c | amino.
|
| k | g or t/u | keto.
|
| s | g or c | strong interactions 3H-bonds.
|
| w | a or t/u | weak interactions 2H-bonds.
|
| b | g or c or t/u | not a.
|
| d | a or g or t/u | not c.
|
| h | a or c or t/u | not g.
|
| v | a or g or c | not t, not u.
|
| n | a or g or c or t/u, unknown, or other | any. |
source: 24 FR 10332, Dec. 22, 1959, unless otherwise noted.