The longest intron rule

Despite the fact that long introns mean an energy and time burden for eukaryotic cells, they play an irreplaceable role in the diversification and regulation of protein production. A general feature is the accumulation of the longest introns closer to the start of protein-coding genes. Our work aimed to more closely characterize the genes in which the longest intron is only located in the second or third third of the gene. Data on the lengths of all introns in genes were extracted from the genomes of 4 vertebrates (human, mouse, chicken and zebrafish), nematode worm and yeast. With the genes divided according to the relative position of the longest intron, gene set enrichment analyses were performed, the results of which were then confronted with the results of randomly generated gene sets of the same size. The analyses show that among the genes associated with biological processes of ion transport across membranes, cell signaling or the development of multicellular organisms, there is a greater representation of genes with the longest intron in the first third. Conversely, among the genes associated with the processes of RNA processing and ribosome biogenesis, there are more genes with the longest intron in the second or third third. It is a newly discovered characteristic with more general validity among multicellular organisms.