Why nature stuck with four letters is one of biology’s fundamental questions. Computers, after all, use a binary system with just two “letters”—0s and 1s.

Chemists Expand Nature's Genetic Alphabet : Shots - Health News DNA's instructions are written in a code of four molecular "letters," labeled A, C, T and G. For the first time, researchers have ...

Discovering Nature's Alphabet Krystina Castella, Brian Boyl, . . Heyday, $15.95 (0pp) ISBN 978-1-59714-021-8 ...

DNA's instructions are written in a code of four molecular "letters," labeled A, C, T and G. For the first time, researchers have created and inserted two brand-new letters into a living cell.