The iron-sulfur protein (Ip) subunit of succinate dehydrogenase (SDH and complex II) of the respiratory chain is highly conserved in evolution [Gould et al., Proc. Natl. Acad. Sci. USA 86 (1989) 1934-1938]. We have cloned the entire human Ip cDNA, as well as the Ip-encoding gene (SDH-B) from two genomic human libraries. The cDNA contains a coding sequence of 840 nt, flanked by a 5'-UTR of 133 nt and a 3'-UTR of 123 nt. The entire transcript is encoded by eight exons within approx. 40 kb. The seven introns range in size from 0.75 kb to > 11 kb, and they appear to be of the 'late' intron class. Approx. 5 kb of upstream sequence was also cloned, and approx. 2.4 kb of the promoter region were sequenced and analyzed for consensus elements binding potential transcription factors and transcriptional activators.