[Molecular mechanisms of the expression of cytosolic and mitochondrial isozyme genes]

We isolated the mouse cytosolic and mitochondrial malate dehydrogenase (cMDH and mMDH) and the mouse cytosolic and mitochondrial aminotransferase (cAspAT and mAspAT) genes functioning in the malate-aspartate shuttle, and localized the DNA regions required for the promoter activity of these isozyme genes. We also characterized nuclear proteins binding to the promoter regions, and found that a transcription factor, CTF/NFI may contribute to the regulation of cMDH, mMDH and cAspAT levels, and that another transcription factor, Sp1 is probably linked to the regulation of mAspAT level. Comparison of the amino acid sequences among the mammalian and bacterial MDHs revealed that the homology between the mouse cMDH and thermophilic bacterial MDH, as well as the homology between the mouse mMDH and E. coli MDH, markedly exceeds the intraspecies sequence homology between cMDH and mMDH from mice. Moreover, structural organizations of the two-pairs of isozyme genes indicated that introns antedate the divergence of these cytosolic and mitochondrial isozyme genes.