Affiliation:
1. Department of Microbiology, Cornell University, Ithaca, New York 14853
Abstract
ABSTRACT
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.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
3 articles.
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