Network model for ISC biogenesis in S. cerevisiae. The letters in the grey circles stand for the different stage of the Biogenesis. A stands for the recovery of Arh1 by Grx5. D stands for the recovery of the dead end complex between Nfs1 and the scaffold by Grx5. F stands for folding. FI stands for Fe import. I stands for the recovery of the scaffolds by Grx5. N stands for Nfs1 recovery by Grx5. R stands for the repair of the clusters. S stands for the synthesis of ISC. St stands for stabilization of the ISC assembled on the scaffolds. T stands for the transfer of the ISC to apo-proteins. The species Apo-P and P in the transfer of a 2Fe2S cluster reaction represent the pairs Apo P1 and P1, Apo P2 and Fe2S2P2 or Fe2S2P2 and P2, respectively. See text and supplementary materials for details and for kinetic representation of the reactions. Dotted arrows represent reactions that have been observed to occur experimentally. Dashed arrows represent the alternative modes of regulatory action for the different proteins. Light grey arrows represent the network interactions that are not likely to exist in the pathway, according to our analysis.