Valid International Union of Biochemistry (IUB) base codes


The following are the official IUB base codes:

Unambiguous bases:

A, C, G &T (or U)

Either of two bases possible:

M (A or C)
R (A or G)
W (A or T/U)
S (C or G)
Y (C or T/U)
K (G or T/U)

Any of three bases possible:

B (C, G or T/U)
D (A, G or T/U)
H (A, C or T/U)
V (A, C or G)

Any of the four bases possible:

N (A, C, G or T/U)

For more information, visit http://www.chem.qmul.ac.uk/iubmb/misc/naseq.html.