Investigating the role of Rrf2 genes : NsrR and RsrR in S. coelicolor and S. venezuelae

• Main Author: Munnoch, John
• Published: University of East Anglia 2016
• Subjects: 579
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.716398

This thesis furthers work on and identifies two Rrf2 regulators with distinct biochemistry and regulons involved in redox homeostasis in S. coelicolor and S. venezuelae. Members of the Rrf2 superfamily of transcription factors are widespread in bacteria and have a range of known regulatory functions including sensing and responding to nitric oxide stress, iron limitation, cysteine availability and the iron sulfur cluster status of the cell. Here we report further study of the Rrf2 protein named NsrR and the identification and characterisation of a novel putative redox sensor RsrR in S. coelicolor and S. venezuelae respectively. NsrR is a global regulator in a range of bacteria, controlling gene expression of a diverse regulon (~35 to >60 genes in B. subtilis and E. coli, respectively) in response to nitrogen stress through a [4Fe-4S] co-factor. We show through ChIP-seq and in vitro DNA-binding studies that NsrR controls only hmpA1, hmpA2 and nsrR by binding to a 11-bp inverted repeat sequence upstream of each gene. Hmp is an NO-detoxifying flavohemoglobin, indicating that NsrR contains a specialised regulon responsible for NO detoxification. We also report an NsrR-independent, NO dependent delay of sporulation in S. coelicolor through an unknown route. RsrR, encoded by a diverse group of actinomycetes, contains an oxygen stable, putative redox-sensing [2Fe-2S] cluster that cycles between an oxidised and reduced state. ChIPseq suggests RsrR binds strongly to an 11-3-11bp inverted repeat to, at least, 16 target sites and more weakly to an 11bp half site at the remaining >100 targets while dRNA-seq indicates a distinctly different set of targets while suggesting the main function of RsrR is regulation of the sven6562 (nmrA) gene, which is transcribed divergently from RsrR. NmrA is a putative LysR-type regulator containing a C-terminal DNA-binding domain and an N-terminal NmrA domain that we hypothesis senses redox poise by binding NAD(P)+ but not NAD(P)H.