Cloning and expression of the human gene for transaldolase. A novel highly repetitive element constitutes an integral part of the coding sequence.

A novel highly repetitive retrotransposable element was cloned based on a limited sequence homology to the human T-cell leukemia virus and a related endogenous retroviral sequence, HRES-1. This repetitive element was found to constitute an integral part of the coding sequence of the human gene for transaldolase. In comparison with the intronless yeast gene, structural analysis of the human transaldolase genomic locus revealed that the human gene is comprised of five exons, second and third of which uniquely developed by insertion of a retrotransposable element. The 1329-base pair full-length cDNA, clone 4/2-4/1, contains an open reading frame coding for a protein of 336 amino acids with a predicted molecular mass of 38 kDa. This protein shows a 58% overall sequence homology with the 37-kDa yeast transaldolase. Antibodies raised against a 22-kDa recombinant polypeptide expressed from a 474-base pair 5' fragment of clone 4/2-4/1, containing repetitive exons 2 and 3, cross-reacted with yeast transaldolase and recognized the 38-kDa native human protein. Detection of a retrotransposon in the coding sequence of the human transaldolase gene demonstrates the importance of these repetitive elements in evolution of the eukaryotic genome.