The Exon Theory of Genes
This extract was created in the absence of an abstract.
Excerpt
Since the intron/exon structure of genes was discovered 10 years ago (Berget et al. 1977; Broker et al. 1977), only a few generalities about the properties of introns have emerged. Most vertebrate genes, but not all, have an intron/exon structure. The length distribution of exons is rather narrow, peaking at about 40 or 50 amino acids. However, introns are an order of magnitude longer than the exons; their length distribution is very broad, the shortest introns being only 50 bases long, the longest extending out to some 50,000 bp. No essential function has been found that requires the presence of all the introns in a gene. If one compares genes from different species, separated by a sufficient evolutionary distance, the exon sequences of homologous genes drift slowly, the positions coding for amino acids being conserved, whereas the intron sequences drift as rapidly as third-base positions, indicating that they are evolutionarily...
