The triosephosphate isomerase gene from maize: introns antedate the plant-animal divergence.

We have cloned and characterized a cDNA and genomic DNA for the triosephosphate isomerase expressed in maize roots. The gene is interrupted by eight introns. If we compare this gene with that for the protein in chicken, which has six introns, we see that five of the introns are at identical places, one has shifted by three codons, and two are totally new. This great matching leads us to conclude that the introns were in place before the plant-animal divergence, and that the parental gene had at least eight introns, two of which were lost in the line that leads to animals.