A novel intron site in the triosephosphate isomerase gene from the mosquito Culex tarsalis

The origin and function of introns in eukaryotic genes has provoked considerable debate since their discovery in 1977. Central to this issue are studies on the highly conserved enzyme, triosephosphate isomerase (TPI, EC 5.3.1.1). The 'introns early' argument suggests that introns are as old as the genes themselves and that the apparent correlation of many of the intron sites in plant, animal and fungal TPI genes with the boundaries of modules is evidence of the assembly of ancient proteins by exon shuffling. In contrast, the 'introns late' view holds that ancient genomes contained few if any introns; introns were inserted into pre-existing genes during the last billion years. We have found that the TPI gene from the mosquito, Culex tarsalis, contains an intron in a unique position that was predicted by W. Gilbert and the exon shuffling hypothesis.