The structural organization of the NDUFS8 gene coding for the TYKY subunit of the human mitochondrial NADH:ubiquinone oxidoreductase (Complex I) has been determined by sequencing of a genomic fragment cloned from a cosmid library. The NDUFS8 gene is located on chromosome 11q13 immediately downstream of the ALDH7 isoform gene. It spans about 6kb and contains seven exons ranging in size from 51 to 186bp. Three CCAAT box sequence motifs are present upstream of the transcription start. Sp1 and NRF1 binding site motifs are present in the first intron. Expression of the gene is ubiquitous but predominant in heart and skeletal muscle. Immunodetection of the TYKY subunit in placental mitochondria after two-dimensional gel electrophoresis revealed that the mature protein has a molecular mass of 22kDa and a pI in the range of 4.9–5.0.