IUPAC Codes
Nucleotides
| Code | Bases | Meaning |
| A | A | Adenine |
| C | C | Cytosine |
| G | G | Guanine |
| T | T | Thymine |
| U | U | Uracil |
| R | A or G | Purine |
| Y | C or T | Pyrimidine |
| S | G or C | Strong |
| W | A or T | Weak |
| K | G or T | Keto |
| M | A or C | Amino |
| B | C, G or T | Not A |
| D | A, G or T | Not C |
| H | A, C or T | Not G |
| V | A, C or G | Not T |
| N | A, C, G or T | Any base |
| - | Gap |
Amino acids
| Code | Three-letter | Name |
| A | Ala | Alanine |
| R | Arg | Arginine |
| N | Asn | Asparagine |
| D | Asp | Aspartic acid |
| C | Cys | Cysteine |
| Q | Gln | Glutamine |
| E | Glu | Glutamic acid |
| G | Gly | Glycine |
| H | His | Histidine |
| I | Ile | Isoleucine |
| L | Leu | Leucine |
| K | Lys | Lysine |
| M | Met | Methionine |
| F | Phe | Phenylalanine |
| P | Pro | Proline |
| S | Ser | Serine |
| T | Thr | Threonine |
| W | Trp | Tryptophan |
| Y | Tyr | Tyrosine |
| V | Val | Valine |
| U | Sec | Selenocysteine |
| O | Pyl | Pyrrolysine |
| B | Asx | Asparagine or aspartic acid |
| Z | Glx | Glutamine or glutamic acid |
| J | Xle | Leucine or isoleucine |
| X | Xaa | Any amino acid |
| * | Ter | Stop |
How to use IUPAC Codes
- The first table lists the nucleotide codes and the bases each one stands for.
- The second lists the amino acid codes with their three-letter codes and names.
Frequently asked questions
What does N mean in a DNA sequence?
Any base: A, C, G or T. It is used where the base is unknown.
What are B, Z and J in a protein?
B is asparagine or aspartic acid, Z is glutamine or glutamic acid, and J is leucine or isoleucine, for when the two cannot be told apart.