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