Characterization of the transcription unit and two processed pseudogenes of chimpanzee triosephosphate isomerase (TPI)

Abstract

Three members of the chimpanzee TPI (encoding triosephosphate isomerase) gene family, the transcription unit and two processed pseudogenes, have been characterized by genomic blotting and nucleotide sequence analysis. The bona fide TPI gene spans 3.5 kb with seven exons and six introns, and is the first hominoid TPI gene to be completely sequenced. The chimpanzee gene exhibits a very high degree of sequence identity with human and rhesus TPI genes. For example, the polypeptides of 248 amino acids (aa) encoded by the chimpanzee and human TPI genes are identical, but the codons for five of these aa differ in the third codon wobble position. No alternative splice sites could be identified in the intervening sequences of the gene and, thus, the molecular basis for the synthesis of the proliferation-specific TPI isozyme observed in hominoids remains elusive. An Alu member occurs upstream from one of the processed pseudogenes, and short sequences with significant identity to the primate LINE-1 element flank the region encompassing the Alu member and TPI pseudogene. A solitary endogenous retroviral long terminal repeat occurs within the structural region of the other processed pseudogene. The ages of the processed pseudogenes are estimated to be 2.6 and 10.4 million years, implying that one was inserted into the genome before and one after the divergence of the chimpanzee and human lineages.