IUPAC nucleotide code

Nucleic acid code Common display Meaning Mnemonic
A A A Adenine
C C C Cytosine
G G G Guanine
T (or U) T T (or U) Thymine (or Uracil)
R A/G A or G Purine
Y C/T C or T (or U) Pyrimidines
K G/T G or T (or U) Bases which are ketones
M A/C A or C Bases with amino groups
S C/G C or G Strong interaction
W A/T A or T (or U) Weak interaction
B C/G/T Not A (i.e. C, G, T or U) B comes after A
D A/G/T Not C (i.e. A, G, T or U) D comes after C
H A/C/T Not G (i.e. A, C, T or U) H comes after G
V A/C/G Neither T nor U (i.e. A, C or G) V comes after U
N A/C/G/T A or C or G or T (or U) Nucleic acid
. or - - Gap of indeterminate length