Fournucleotide

Fournucleotide is a term used in speculative discussions of nucleic acid chemistry to denote a hypothetical monomer that carries four distinct nucleobases within a single unit, in contrast to natural nucleotides that carry one base (adenine, thymine or uracil, cytosine, and guanine). The concept envisions a single, polymerizable unit capable of encoding more information per monomer than standard nucleotides, with potential applications in high-density genetic storage or expanded genetic codes. The term is not part of standard nomenclature and has no widely accepted chemical realization.

Concept and design: In theoretical designs, a four-base monomer could be created by combining four different base moieties onto a central sugar-phosphate scaffold or by using a branching or multiplexed base structure. Implementing such a unit would require new pairing rules and polymerases capable of processing the quad-base monomer. Although researchers have pursued expanded genetic alphabets by adding unnatural bases that pair selectively, a true four-base monomer remains an extrapolation that has not been demonstrated in practice.

Status and challenges: Major obstacles include chemical stability, scalable synthesis, fidelity of replication and transcription, and compatibility with cellular machinery. Potential advantages include higher information density for data storage and the possibility of encoding additional amino acids, but these benefits are speculative and contingent on overcoming substantial technical barriers.

See also: Expanded genetic code; Unnatural base pair; Synthetic biology; DNA data storage.