Figure 1

Schematic representation of the minichromosomes encoding the hydrogenase (a) and the "mitochondrial" 24 and 51 kDa genes (b). The macronuclear minichromosomes are capped by telomeres (T) and contain non-coding DNA sequences (N) at the N- and C-terminal parts of the chromosome. A mitochondrial targeting signal (M) is found at the N terminal part of the coding sequence. 1. a. The hydrogenase is chimeric, i.e. it consists of a long-type [FeFe] hydrogenase with 4 FeS clusters (black bars in HDG), a 24 kDa (hoxF) module ("24") with an N1a type FeS cluster, and a 51 kDa (hoxU) ("51") module with a N3-type [4Fe-4S] cluster plus a FMN and a NAD binding site. 1. b. The subunits of the "mitochondrial" complex I are localized on individual minichromosomes. They each possess a mitochondrial targeting signal (M) and upstream and downstream non-coding DNA (N). The "mitochondrial" 51 kDa module possesses two small introns (arrows) that are absent from the correspondent hydrogenase module.