English: Two different cytosolic iron-sulfur protein assembly (CIA) machineries in Guillardia theta. Host (cytosol) and symbiont (periplastidial compartment, PPC) specific version of CIA machineries are shown schematically. The cytosolic CIA machinery builds iron-sulfur clusters and is dependent on a so far not identified sulfur component (X-S) provided by the mitochondrial ISC. In case of PPC located CIA this X-S may be provided by the plastidal SUF machinery. Identified factors are shown in blue, factors which could not be identified are shown in transparent. Red/yellow spheres represent [4Fe-4S] and [2Fe-2S] clusters. Nbp35/Cfd1 or Npb35 multimers are scaffolds for iron-sulfur Cluster formation and their function is dependent on [4Fe-4S] cluster binding. In turn, the maturation of these multimers is dependent on the electron transfer system build by Tah18-Dre2, the latter also complexed with [2Fe-2S] clusters. Apo-proteins are loaded with iron-sulfur clusters via Nar1 by the Mms19-Cia1-Cia2 targeting complex. Grx3/Grx4 have been shown to be involved in iron-sulfur cluster formation but their precise role is not fully understood. Possibly, only one Grx is present in the cytosol and the PPC of G. theta.