How big can a gene be? Ten years ago in the early days of genome sequencing, researchers scoured the genomes of 580 bacterial and archaeal species for large genes. They found that 0.2% of all genes identified are longer than 5,000 bases and 80 of them are “giant genes,” those larger than 15,000 bases. To put this in perspective, the average prokaryotic gene length is between 900 and 1,200 bases.
The two longest genes were found in the green sulfur bacterium Chlorobium chlorochromatii CaD3. The genes encode proteins 36,806 and 20,647 amino acids long and their corresponding genes would be 110,418 and 61,941 bases long, respectively. At the time of this research, these giant genes are only surpassed in length by the human titin coding sequence which is 38,138 amino acids long. Now, scientists have identified a slew of genes that exceed one million bases long. (more…)