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J. Biol. Chem., Vol. 277, Issue 8, 5866-5874, February 22, 2002

This Article Full Text Full Text (PDF) All Versions of this Article: 277/8/5866    most recent M110555200v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Akakura, R. Articles by Winans, S. C. Search for Related Content PubMed PubMed Citation Articles by Akakura, R. Articles by Winans, S. C.

Constitutive Mutations of the OccR Regulatory Protein Affect DNA Bending in Response to Metabolites Released from Plant Tumors^*

Reiko Akakura and Stephen C. Winans

From the Department of Microbiology, Cornell University, Ithaca, New York 14853

OccR is a LysR-type transcriptional regulator of Agrobacterium tumefaciens that positively regulates the octopine catabolism operon of the Ti plasmid and is also an autorepressor. Positive control of the occ genes occurs in response to octopine, a nutrient released from crown gall tumors. OccR binds to a site upstream of the occQ promoter in the presence and absence of octopine. Octopine causes prebound OccR to undergo a conformational change at the DNA binding site that causes changes in footprint length and DNA bending. To determine the roles of these conformational changes in transcriptional activation, we isolated 22 OccR mutants that were able to activate the occQ promoter in the absence of octopine. Thirteen of these mutants contained single amino acid substitutions, and nine contained two base pair changes resulting in two amino acid substitutions, which in most cases acted synergistically. These mutations spanned the entire length of the protein. Most of these mutant proteins in the absence of octopine displayed DNA binding and bending properties characteristic of transcriptionally active OccR-octopine complexes.

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