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J. Bacteriol., May 1995, 2343-2353, Vol 177, No. 9
MM Hryniewicz and NM Kredich
CysB is a transcriptional activator for the cysteine regulon and negatively
autoregulates its own gene, cysB. Transcription activation also requires an
inducer, N-acetyl-L-serine. CysB is known to bind to activation sites just
upstream of the -35 regions of the positively regulated cysJIH, cysK, and
cysP promoters and to a repressor site centered at about +1 in the cysB
promoter. Additional accessory sites have been found in positively
regulated promoters. The hydroxyl radical footprinting experiments reported
here indicate that the activation sites CBS-J1, CBS-K1, and CBS-P1 in the
cysJIH, cysK, and cysP promoters are composed of two convergently oriented
19-bp half-sites separated by 1 or 2 bp. N-Acetyl-L-serine stimulates
binding to these sites as well as to the accessory sites CBS-J2 and CBS-P2,
both of which share a similar topology with activation sites. A second
topology is found in the accessory site CBS-K2 and the repressor site
CBS-B, which contain divergently oriented 19-bp half-sites separated by one
or two helical turns. N-Acetyl-L-serine inhibits binding to these two
sites. A third topology is present in the cysK and cysP promoters, where an
additional half-site is oriented toward the activation site and separated
from it by one helical turn. Here, CysB binds to all three half-sites,
bending the DNA, and N-acetyl-L-serine decreases the extent of bending. The
marked dissimilarities of these half-site arrangements and of their
responses to N-acetyl-L-serine suggest that CysB, a homotetramer, binds to
them with different combinations of subunits.
Copyright © 1995, American Society for Microbiology
Hydroxyl radical footprints and half-site arrangements of binding sites for the CysB transcriptional activator of Salmonella typhimurium
Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710, USA.
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