Most mutant OccR proteins that are defective in positive control hold operator DNA in a locked high-angle bend

J Bacteriol. 2011 Oct;193(19):5442-9. doi: 10.1128/JB.05352-11. Epub 2011 Jul 29.


OccR is a LysR-type transcriptional regulator of Agrobacterium tumefaciens that positively regulates the octopine catabolism operon of the Ti plasmid. Positive control of the occ genes occurs in response to octopine, a nutrient released from crown gall tumors. OccR also functions as an autorepressor in the presence or absence of octopine. OccR binds to a site between occQ and occR in the presence or absence of octopine, although octopine triggers a conformational change that shortens the DNA footprint and relaxes a DNA bend. In order to determine the roles of this conformational change in transcriptional activation, we isolated 11 OccR mutants that were defective in activation of the occQ promoter but were still capable of autorepression. The mutations in these mutants spanned most of the length of the protein. Two additional positive-control mutants were isolated using site-directed mutagenesis. Twelve mutant proteins displayed a high-angle DNA bend in the presence or absence of octopine. One mutant, the L26A mutant, showed ligand-responsive DNA binding similar to that of wild-type OccR and therefore must be impaired in a subsequent step in activation.

MeSH terms

  • Agrobacterium tumefaciens / drug effects
  • Agrobacterium tumefaciens / genetics
  • Agrobacterium tumefaciens / metabolism*
  • Arginine / analogs & derivatives
  • Arginine / pharmacology
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism*
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism
  • Mutagenesis, Site-Directed
  • Mutation
  • Promoter Regions, Genetic / genetics
  • Transcription Factors / genetics
  • Transcription Factors / metabolism*


  • Bacterial Proteins
  • Carrier Proteins
  • DNA-Binding Proteins
  • Membrane Proteins
  • OccQ protein, Agrobacterium tumefaciens
  • Transcription Factors
  • OccR protein, Bacteria
  • octopine
  • Arginine