IUPAC codes for sequence wildcard letters

Nucleotide
Symbol  Meaning
A  Adenine
C  Cytosine
G  Guanine
T  Thymine
U  Uracil
M  A or C
R  A or G
W  A or T
S  C or G
Y  C or T
K  G or T
V  A or C or G
H  A or C or T
D  A or G or T
B  C or G or T
X  G or A or T or C
N  G or A or T or C

Protein
Symbol Meaning
X Any amino acid
B N or D
Z Q or E

Reference
Cornish-Bowden (1985) , IUPAC-IUB symbols for nucleotide nomenclature, Nucl. Acids Res . 13: 3021-3030.