Abstract
In
Salmonella enterica
, tricarballylate (Tcb) catabolism requires function of TcuB, a membrane-bound protein that contains [4Fe-4S] clusters and heme. TcuB transfers electrons from reduced flavin adenine dinucleotide in the Tcb dehydrogenase (TcuA) to electron acceptors in the membrane. We recently showed that functions needed to assemble [Fe-S] clusters (i.e., the
iscRSUA-hscBA-fdx
operon) compensate for the lack of ApbC during growth of an
apbC
strain on Tcb. ApbC had been linked to [Fe-S] cluster metabolism, and we showed that an
apbC
strain had decreased TcuB activity. Here we report findings that expand our understanding of the regulation of expression of the
iscRSUA
genes in
Salmonella enterica
. We investigated why low levels of glucose or other saccharides restored growth of an
apbC
strain on Tcb. Here we report the following findings. (i) A ≤1 mM concentration of glucose, fructose, ribose, or glycerol restores growth of an
apbC
strain on Tcb. (ii) The saccharide effect results in increased levels of TcuB activity. (iii) The saccharide effect depends on the global regulatory protein Cra. (iv) Putative Cra binding sites are present in the regulatory region of the
iscRSUA
operon. (v) Cra protein binds to all three sites in the
iscRSUA
promoter region in a concentration-dependent fashion. To our knowledge, this is the first report of the involvement of Cra in [Fe-S] cluster assembly.