Human triosephosphate isomerase cDNA and protein structure. Studies of triosephosphate isomerase deficiency in man

Nine cDNA clones of human adult liver triosephosphate (TP) isomerase have been isolated and characterized. All nine appear to be derived from a single mRNA species. DNA sequencing of one clone, designated pHTPI-5a, defined the last two nucleotides of the methionine initiation codon, the entire 744-nucleotide coding region of the mature polypeptide, and the entire 448-nucleotide 3' untranslated region. The frequency of TP isomerase clones in the cDNA library suggests that TP isomerase mRNA is present in adult liver at approximately 25 copies/cell. A single, low abundance TP isomerase mRNA species was detected in RNA isolated from normal human fibroblast cell lines. Analysis of TP isomerase mRNA levels in cultured fibroblasts of individuals that are homozygous for TP isomerase deficiency revealed normal levels in one and approximately 40% of normal levels in another. From this small patient sampling, it can be concluded that the genetic basis for TP isomerase deficiency is heterogeneous.