The role of error-coding in shaping the nucleotide alphabet: nature´s choice of A,U, C and G

The paper summarizes a proposed role for error-coding in shaping the composition of the natural nucleotide alphabet. It is argued that as nucleotide replication is essentially an information transmission phenomenon, the evolutionary pressures shaping alphabet composition might not have been confined to physicochemical issues alone, and that error-coding might have had a constraining evolutionary role. Nucleotide recognition features are mapped to 4-digit binary numbers, capturing the hydrogen donor/acceptor patterns (3-bits) and the purine/pyrimidine size motif (1-bit). An error-coding analysis, treating potential alphabets as combinations of 4-bit codewords, suggests that optimal alphabets are composed of nucleotides in which the purine/pyrimidine feature relates to the donor/acceptor pattern as a parity bit. Thus, of sixteen possible informationally distinct nucleotides, a viable alphabet, subject to error-coding constraints, may draw from either one of two sets of eight same-parity nucleotides, but not from both. Chemical considerations such as tautomeric instability, and vulnerability to hydrolysis, render several potential nucleotides unsuitable, reducing the size of the available sets. Two solutions emerge; one corresponds precisely to the natural alphabet of A, C, G and T. A second, less favored solution also appears viable, offering the possibility of life based on an alternative alphabet.