Spx

• Description: transcriptional regulator Spx, involved in regulation of many genes.
  
  

Gene name	spx
Synonyms	yjbD
Essential	no
Product	transcriptional regulator Spx
Function	negative and positive regulator of many genes
Metabolic function and regulation of this protein in SubtiPathways: Riboflavin / FAD
MW, pI	15,5 kDa, 7.80
Gene length, protein length	393 bp, 131 amino acids
Immediate neighbours	yjbC, yjbE
Get the DNA and protein sequences (Barbe et al., 2009)
Genetic context This image was kindly provided by SubtiList

The gene

Basic information

• Locus tag: BSU11500

Phenotypes of a mutant

Loss of up-regulation of the methionine sulfoxide reductase (msrA-msrB) operon in response to thiol specific oxidative stress, also loss of trxA and trxB upregulation in response to thiol specific oxidative stress.

Database entries

• DBTBS entry: [1]

• SubtiList entry: link

The protein

Basic information/ Evolution

• Catalyzed reaction/ biological activity:
  • transcriptional regulator of many genes in response to thiol specific oxidative stress (transcription activator of trxA and trxB)
  • in addition, Spx inhibits transcription by binding to the C-terminal domain of the alpha subunit of RNAP (RpoA), disrupting complex formation between RNAP and certain transcriptional activator proteins like ResD and ComA
  • in response to thiol specific oxidative stress, Spx can also activate transcription, making it a general regulator that exerts both positive and negative control over transcription initiation
  • involved in competence regulation PubMed

• Protein family: Spx subfamily (according to Swiss-Prot) Arsenate Reductase (ArsC) family, Spx subfamily

• Paralogous protein(s): MgsR

Extended information on the protein

• Kinetic information:

• Domains: CXXC (10-13): Acts as a disulfide switch for the redox-sensitive transcriptional regulation of genes that function in thiol homeostasis.

• Modification: Cysteine oxidation of the CXXC motif

• Cofactor(s):

• Effectors of protein activity:

• Interactions: Spx-YjbH PubMed, Spx-RpoA (C-terminal domain PubMed)

• Localization: cytoplasm (according to Swiss-Prot)

Database entries

• Structure: 1Z3E complex with C-terminal domain of RpoA NCBI

• UniProt: O31602

• KEGG entry: [2]

• E.C. number:

Expression and regulation

• Operon:
  • yjbC-spx PubMed
  • spx PubMed

• Sigma factor:
  • four promoters upstream of yjbC: SigW, SigB, SigX PubMed, SigM PubMed
  • promoters upstream of spx: SigA, SigW PubMed, SigM PubMed

• Regulation:
  • induced by stress (SigB) PubMed
  • transcription is represed by PerR and YodB PubMed
  • repressed in the absence of hydrogen peroxide (PerR) PubMed
  • upregulated in response to enduracidin PubMed

• Regulatory mechanism: transcription repression
  • PerR: transcription repression PubMed

• Additional information:
  • post-translational control by ClpX-ClpP: Spx naturally contains a C-terminal sequence that resembles the SsrA tag and targets the protein for degradation. PubMed
  • proteolysis is enhanced by YjbH. PubMed

Biological materials

• Mutant: ORB6781 (spc), ORB6876 (tet), available in Zuber lab, also available in the Stülke lab

• Expression vector:

• lacZ fusion:

• GFP fusion:

• two-hybrid system: B. pertussis adenylate cyclase-based bacterial two hybrid system (BACTH), available in Stülke lab

• Antibody:

Labs working on this gene/protein

Peter Zuber, Oregon Health and Science University, USA Homepage

Richard Brennan, Houston, Texas, USA Homepage