This can clearly distinguish the four DNA letters, A, C, G and T.

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The G-quadruplex seems to form in DNA where guanine exists in substantial quantities.

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Embedded in each set of 23 chromosomes are 3 billion base pairs of DNA, known by the letters A, T, C and G, for the chemical bases adenine, thymine, cytosine and guanine.

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The codons were written in a four-letter alphabet, A, C, G, T, that abbreviated the names of the chemicals of which DNA is made.

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