Abstract

The iron-sulfur protein (Ip) subunit of succinate dehydrogenase (and complex II of the electron transport chain) is highly conserved in evolution [Gould et al., Proc. Natl. Acad. Sci. USA 86 (1989) 1934–1938]. We have cloned the Drosophila melanogaster Ip-encoding gene (SdhB) by genomic library screening using the human Ip-encoding cDNA as a probe at low stringency. A 2.7-kb fragment containing SdhB has been sequenced and shown to comprise the entire transcribed region and more than 900 bp of promoter region. The gene contains three exons and two small introns of 272 and 56 nt, respectively, and is transcribed into an mRNA of 1205 nt (plus poly(A) tail). The deduced amino-acid (aa) sequence shows strong similarities with Ip peptides from Escherichia coli, yeasts, plants and mammals, with 100% aa identity around the three Cys clusters which form the non-heme iron-sulfur centers. In situ hybridization on polytene chromosomes maps SdhB to band 42D 1–5 on the right arm of the second chromosome next to the centromere. Developmental and tissue-specific Northern blots show a single transcript of 1.3 kb in all tissues. However, its abundance varies during development and in the major body segments of the adult fly. Pupae have very low levels of transcript, in contrast to larvae. It is most abundant in the adult thorax and low in abdominal tissues.

Keywords: Mitochondria; electron transport chain; complex II; respiration

Abbreviations: aa, amino acid(s); bp, base pair(s); D., Drosophila; Fp, flavoprotein; GCG, Genetics Computer Group (Madison, WI, USA); Ip, iron sulfur protein(s); kb, kilobase(s) or 1000 bp; mt, mitochondrial; nt, nucleotide(s); oligo, oligodeoxyribonucleotide; ORF, open reading frame; RACE, rapid amplification of cDNA ends (Frohman et al., 1988); SdhB, gene encoding Ip; SDH, succinate dehydrogenase; tsp, transcription start point(s); UTR, untranslated region(s)