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. 2004 Feb 27;32(4):1448–1459. doi: 10.1093/nar/gkh315

Figure 3.

Figure 3

Approaches to randomizing synthetic DNA. Examples show randomization of one codon with mixed nucleotides (NNN, NNT/C, NNG/T or NNT/G/C) and with trinucleotide phosphoramidites. Synthesis in all three cases commences conventionally 3′ of the randomized codon. At the 3′-end of the randomized codon (A) all four nucleotides, (B) a mixture of T and C, (C) a mixture of G and T or (D) a mixture of T, G and C can be added. In each case a mixture of all four nucleotides is added at each of the remaining two positions. Having a mixture of G and C at the 3′-end of the codon will provide 32 codons, all 20 amino acids and one stop codon. (E) Conversely, the codon can be synthesized by the direct addition of a mixture of 20 trinucleotide phosphoramidites in one step. ALA–TRP represent 20 presynthesized 3-nt codons, one to code for each amino acid.