Intron existence predated the divergence of eukaryotes and prokaryotes.

Nucleotide sequences for the nuclear genes encoding chloroplast (GapA and GapB) and cytosolic (GapC) glyceraldehyde-3-phosphate dehydrogenases (GAPDHs) from Arabidopsis thaliana were determined. Comparison of nucleotide sequences indicates that the divergence of chloroplast and cytosolic GAPDH genes preceded the divergence of prokaryotes and eukaryotes. In addition, some intron-exon junctions are conserved among GapB, GapC, and chicken GAPDH genes. These results provide evidence at the molecular level to support the idea that introns existed before the divergence of prokaryotes and eukaryotes.