The transcriptional regulator TamR from Streptomyces coelicolor controls a key step in central metabolism during oxidative stress.

Multiple antibiotic resistance regulator (MarR) family transcriptional regulators usually regulate gene activity by responding to specific ligands. Here we show that TamR (trans-aconitate methyltransferase regulator), a MarR homologue from Streptomyces coelicolor, functions in oxidative stress responses to regulate a key step in central metabolism. The gene encoding TamR is oriented divergently from the tam gene, which encodes trans-aconitate methyltransferase. Trans-aconitate methyltransferase methylates trans-aconitate, which is formed when cis-aconitate is released during aconitase-mediated isomerization of citrate to isocitrate; trans-aconitate, but not its methyl ester, is a potent inhibitor of aconitase. We show that TamR binds with high affinity to the intergenic region between the tamR and tam genes. Notably, trans-aconitate attenuates DNA-binding by TamR, as do citrate, cis-aconitate and isocitrate, which are the substrate, intermediate and product of aconitase respectively. In vivo, hydrogen peroxide and citrate induce significant upregulation of the tam (SCO3132), tamR (SCO3133) and aconitase (SCO5999) genes. Since oxidative stress leads to disassembly of the [4Fe-4S] cluster that is essential for aconitase activity, resulting in accumulation of citrate and release of cis-aconitate and its subsequent conversion to trans-aconitate, we propose that TamR mediates a novel regulatory function in which the inhibitory effects of trans-aconitate and accumulated citrate are alleviated.