Regulatory regions of the mitochondrial and cytosolic isoenzyme genes participating in the malate-aspartate shuttle

The malate-aspartate shuttle, consisting of mitochondrial and cytosolic aspartate aminotransferase and mitochondrial and cytosolic malate dehydrogenase, is a major pathway for the transport of reducing equivalents from cytosol to mitochondria in mammals. To elucidate molecular mechanisms regulating metabolic coordination between the mitochondria and the cytosol, we analyzed the 5'-flanking regulatory regions of the complete set of mouse isoenzyme genes playing a pivotal role in the shutle. Deletion analysis and an in vivo transfection assay, using NIH3T3 cells, revealed that all the promoter regions are located within the 300-base pair regions upstream from the initiation codon. Subsequently, DNase I footprinting analyses using NIH3T3 cell nuclear extracts led to identification of several protein binding sites within these promoter regions. A synthetic oligomer containing the consensus binding site sequence for CTF/NFI, a transcription factor for RNA polymerase II, competed for the binding of proteins to the promoter regions of cytosolic aspartate aminotransferase and mitochondrial and cytosolic malate dehydrogenase genes, but not for that of the mitochondrial aspartate aminotransferase gene. On the other hand, a synthetic oligomer containing the consensus binding site sequence for Sp1, which activates transcription from promoters containing properly positioned GC boxes, competed for protein(s) binding to the promoter region of the mitochondrial aspartate aminotransferase gene.