, 2002; Lill, 2009; Py & Barras, 2010), which may explain the lethal pattern observed. To confirm this ISC specificity, E. coli iscS mutant strains were tested for ISC complementation, in which sufCDSUB, sufS, or sufS plus the putative desulfurase activator sufU plasmids was unable to complement ISC as well. This result agrees with

data described above: indeed, neither sufCDSUB or any other gene alone is able to complement Proteobacteria ISC elements, demonstrating the conservancy of the ISC system. Escherichia coli iscS mutants were chosen for this type of experiment because the auxotrophic phenotype can be distinguished by supplemented media and parental INCB024360 molecular weight strains, and because it also permits the verification of complementation on further deletions, as verified for the SUF system. Because the E. Apoptosis inhibitor faecalis operon shares major ortholog elements with the SUF system, we verified the possibility of E. coli sufABCDSE complementation. Escherichia coliΔiscS∷Tn10∷ΔABCDSE complemented with sufCDSUB was

able to grow on Luria broth plates containing arabinose. It was also able to grow on M9-glycerol modified media in the absence of iscS, albeit with a weaker phenotype and requiring 48 h to grow. In this way, the entire sufCDSUB could complement the whole sufABCDSE system, not just replacing this system but also contributing to maturation of proteins linked to the ISC system, perhaps due to the presence of SufU and its [Fe–S] cluster assembly characteristics similar to IscU. As Adenosine the entire sufCDSUB system is able to provide viable E. coli strains, it is able to perform the necessary functions for nicotinic acid and thiamine homeostasis and the relevant processes in [Fe–S] cluster homeostasis. However,

sufCDSUB is not able to complement E. coliΔiscS strains (Fig. 3a). This may be related to the presence of E. coli SUF components, in which protein complexes are essential for proper SUF function in E. coli. The presence of these elements and/or complexes could be either inhibiting or obstructing the actuation of the in trans operon. This hypothesis is based on data found in this work, where (1) neither E. coliΔiscS∷ΔsufS or E. coliΔiscS∷ΔsufSE could be complemented by sufS, sufSU, or sufCDSUB, and (2) E. faecalis sufCDSUB was not able to complement E. coliΔiscS strains but could complement E. coliΔiscSΔsufABCDSE. In fact, several specific protein–protein interactions involving E. coli SUF system partners have been described: SufE and SufBCD acting synergistically to modulate SufS activity (Outten et al.