Single Letter Codes

Restriction enzymes recognize nucleotides (or bases) A (Adenine), C (Cytosine), G (Guanine), or T (Thymine). The following IUPAC (International Union of Pure and Applied Chemistry) single letter codes are used to designate more than one nucleotide:

• B = C or G or T 
• D = A or G or T 
• H = A or C or T 
• K = G or T 
• M = A or C 
• N = A or C or G or T 
• R = A or G 
• S = C or G 
• V = A or C or G 
• W = A or T 
• Y = C or T