Complex II of mitochondria contains succinate dehydrogenase and subunits to link this enzyme directly to the inner mitochondrial membrane. The four peptides of this complex are the flavoprotein (Fp) and iron-sulfur protein (Ip) of the dehydrogenase, and two integral membrane proteins referred to as C(II-3) and C(II-4). Their respective genes in mammals are SDHA, SDHB, SDHC and SDHD) in order of decreasing molecular weights of the peptides. In this paper we describe the identification of two pseudogenes and the complete characterization and mapping of the active SDHC gene in humans. The active gene, encoding a small peptide of 15.5 kDa, has six exons and five introns extending over 35 kb. It has been mapped at position 1q21, adjacent to the pericentric heterochromatin on the long arm of chromosome 1. Approximately I kb of the promoter region has also been sequenced and examined for sequence motifs suggesting the binding of known transcription factors. Several potential sites for the nuclear respiratory factors NRF-1 and NRF-2 were identified.
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