TPI1 encodes an enzyme, consisting of two identical proteins, which catalyzes the isomerization of glyceraldehydes 3-phosphate (G3P) and dihydroxy-acetone phosphate (DHAP) in glycolysis and gluconeogenesis. Mutations in this gene are associated with triosephosphate isomerase deficiency. Pseudogenes have been identified on chromosomes 1, 4, 6 and 7. Alternative splicing results in multiple transcript variants.

Spliceosomal introns are present in the nuclear protein-coding genes of most eukaryotic organisms, but they have not been detected in several eukaryotic protist phyla or in eubacteria, archaebacteria, and organelles. Two major theories had emerged in the continuing debate on the origin of these introns.