IUPAC Nucleotide Codes
The International Union of Pure and Applied Chemistry (IUPAC) code provides the nomenclature for a single or set of nucleotide bases for representing biological concepts such as nucleotide degeneracy and single base variations in sequences.
IUPAC codes are useful to represent a sequence if there is uncertainty about a nucleotide at a given position. For example, to represent the sequence for possible single nucleotide polymorphisms.
The other use of IUPAC codes could be estimating the nucleotide sequence from the protein sequence due to codon degeneracy (if the nucleotide sequence is unknown for that gene).
IUPAC codes for single nucleotides
| IUPAC code | Nucleotide bases | Complementary Base |
|---|---|---|
| A | A (Adenine) | T |
| C | C (Cytosine) | G |
| G | G (Guanine) | C |
| T | T (Thymine ) | A |
| U | U (Uracil) | A |
IUPAC codes for nucleotide degeneracy (Wobbles)
| IUPAC code | Nucleotide bases | Complementary code |
|---|---|---|
| R | A or G (Purines) | Y |
| Y | C or T/U (Pyrimidines) | R |
| M | A or C (Amino group) | K |
| K | G or T/U (Keto group) | M |
| S | C or G | S |
| W | A or T/U | W |
| H | A or C or T/U | D |
| B | C or G or T/U | V |
| V | A or C or G | B |
| D | A or G or T/U | H |
| N | A or G or C or T/U (any other base) | N |
| - | Gap | - |
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