Molecular cloning and expression analysis of the rice triose phosphate/phosphate translocator gene

The triose phosphate/phosphate translocator (TPT) is located in the inner envelope membrane of plant chloroplast. It catalyzes the counter exchange of triose phosphate/3-phosphoglycerate for phosphate. To reveal the relationship between the TPT structure and its function, a cDNA encoding the complete precursor of TPT has been isolated from rice by using RT-PCR and rapid amplification of cDNA ends (RACE) strategies. The rice tpt was identified as a single copy gene by using Southern blotting. And it was mapped to chromosome 1. The rice TPT mRNA encodes a precursor protein of 417 amino acids with a deduced molecular weight of 44 kDa. A putative processing site between Ala-95 and Ala-96 of the precursor protein was suggested by comparison with the TPTs from spinach and maize. Therefore, the mature part of rice TPT consists of 322 amino acid residues with a molecular weight of 35 kDa. It shares 89% homology with maize and 93% with wheat. But the transit peptide and about 20 amino acids at N-end of the mature part showed a much lower homology to other plant TPTs. The mature protein exhibits high hydrophobicity and consists of seven transmembrane regions. High expression level of the TPT mRNA was detected in tissues such as leaf and coleoptile, while no apparent expression was detected in root and seed. These indicated the expression of rice TPT might be restricted to green tissues. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.