E. Szathmary, WHAT IS THE OPTIMUM SIZE FOR THE GENETIC ALPHABET, Proceedings of the National Academy of Sciences of the United Statesof America, 89(7), 1992, pp. 2614-2618
An important question in biology is why the genetic alphabet is made o
f just two base pairs (G.C and A.T). This is particularly interesting
because of the recent demonstration [Piccirilli, J. A., Krauch, T., Mo
roney, S. E. & Benner, S. A. (1990) Nature (London) 343, 33-37] that t
he alphabet can in principle be larger. It is possible to explain the
size of the present genetic alphabet as a frozen character state that
was an evolutionary optimum in an RNA world when nucleic acids functio
ned both for storing genetic information and for expressing informatio
n as enzymatically active RNA molecules-i.e., ribozymes. A previous mo
del [Szathmary, E. (1991) Proc. R. Soc. London Ser. B 245, 91-99] has
described the principle of this approach. The present paper confirms a
nd extends these results by showing explicitly the ways in which copyi
ng fidelity and metabolic efficiency change with the size of the genet
ic alphabet.