Exons and Introns

Abstract

If genome space is finite with little, if any, DNA that is not functional under some circumstance, then potential conflicts between different forms of genomic information must be resolved by appropriate trade-offs. These trade-offs sometimes require that genes accommodate spacers, introns, and simple sequence elements. The nature and extent of the trade-offs varies with the biological species. Study of trade-offs is facilitated in genes or species where demands are exceptional (e.g. genes under positive selection pressure to adapt proteins, genes that overlap, and species under extreme downward or upward GC-pressures). Spacers and introns are likely to have existed early in evolution because they are preferential sites for the stem-loop structures that are necessary for initiating recombination and, hence, error-detection and correction. Genes, as recognized today, would have arisen in sequences already adapted for these purposes. Purine-loading pressure would have supported protein-pressure in provoking the splitting into introns of what might otherwise have been large exons. From this perspective we can understand why the genes of the malaria parasite are extraordinarily long, and we can identify the potential Achilles heel of the AIDS virus as the dimer-linkage sequence that is essential for the copackaging of disparate genomes, so allowing recombination repair in a future host.

Ideas in the theory of evolution can be used in situations far removed from biology. Similarly, information theory has ideas that are widely applicable to situations remote from its original inspiration.

Richard Hamming (1980) [1]