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XapR DNA-binding transcriptional activator

Synonyms: XapR-xanthosine, XapR
The XapR protein belongs to the LysR family of transcriptional regulators. It activates transcription of the xapAB operon [1]. Both xanthosine and deoxyinosine can function as an inducer [3]. An xapR mutant can not grow on xanthosine [1].

Transcription factor      
TF conformation(s):
Name Conformation Type TF-Effector Interaction Type Apo/Holo Conformation Evidence (Confirmed, Strong, Weak) References
XapR Functional   Apo [BPP] [1]
XapR-xanthosine Functional Allosteric Holo [BPP], [GEA], [HIFS], [IEP] [1], [2], [3]
Evolutionary Family: LysR
Sensing class: External sensing using transported metabolites
Connectivity class: Local Regulator
Gene name: xapR
  Genome position: 2521593-2522477
  Length: 885 bp / 294 aa
Operon name: xapR
TU(s) encoding the TF:
Transcription unit        Promoter

Regulated gene(s) xapA, xapB
Multifun term(s) of regulated gene(s) MultiFun Term (List of genes associated to the multifun term)
nucleotide and nucleoside conversions (1)
carbon compounds (1)
Porters (Uni-, Sym- and Antiporters) (1)
membrane (1)
Regulated operon(s) xapAB
First gene in the operon(s) xapA
Simple and complex regulons XapR
Simple and complex regulatory phrases Regulatory phrase (List of promoters regulated by the phrase)

Transcription factor regulation    

Transcription factor binding sites (TFBSs) arrangements

  Functional conformation Function Promoter Sigma factor Central Rel-Pos Distance to first Gene Genes Sequence
LeftPos RightPos Evidence (Confirmed, Strong, Weak) References
  XapR-xanthosine activator xapAp Sigma70, Sigma38 -119.0 -151.0 xapA, xapB
2525023 2525035 [GEA], [HIBSCS] [1], [3]
  XapR-xanthosine activator xapAp Sigma70, Sigma38 -39.0 -71.0 xapA, xapB
2524943 2524955 [GEA], [HIBSCS] [1], [3]

Evolutionary conservation of regulatory elements    
     Note: Evolutionary conservation of regulatory interactions and promoters is limited to gammaproteobacteria.
Promoter-target gene evolutionary conservation


 [BPP] Binding of purified proteins

 [GEA] Gene expression analysis

 [HIFS] Human inference of function from sequence

 [IEP] Inferred from expression pattern

 [HIBSCS] Human inference based on similarity to consensus sequences


 [1] Seeger C., Poulsen C., Dandanell G., 1995, Identification and characterization of genes (xapA, xapB, and xapR) involved in xanthosine catabolism in Escherichia coli., J Bacteriol 177(19):5506-16

 [2] Brun YV., Breton R., Lanouette P., Lapointe J., 1990, Precise mapping and comparison of two evolutionarily related regions of the Escherichia coli K-12 chromosome. Evolution of valU and lysT from an ancestral tRNA operon., J Mol Biol 214(4):825-43

 [3] Jorgensen C., Dandanell G., 1999, Isolation and characterization of mutations in the Escherichia coli regulatory protein XapR., J Bacteriol 181(14):4397-403