Final full-text version of the paper available at: http://nar.oxfordjournals.org/cgi/content/abstract/20/7/1755 .-- Copyright © by Oxford University Press. -- Http://nar.oxfordjournals.org/
The xyIR and xylS genes, which encode the positive
regulators of the TOL plasmid catabolic pathways, are
adjacent genes on the TOL plasmid and are transcribed
from divergent promoters. Transcription from the xylS
gene promoter, Ps, is positively regulated by effectoractivated
XyIR protein and requires the specific RNA
polymerase sigma54 subunit (RpoN). Deletions and
point mutations in the Ps upstream region localized the
site of XyIR interaction to the region between - 133 bp
and - 207 bp (with respect to the transcriptional start
of the xylS messenger), which contains an inverted
sequence repeat largely homologous to the motif
recognised by XyIR in the XyIR-regulated 'upper'
catabolic pathway promoter, Pu. Gel retardation
experiments showed binding of IHF to the Ps promoter
region. Corresponding sequences showing good
homology to the IHF-binding consensus were identified
close to the Ps Promoter (between - 35 bp and - 47
bp, Ps proximal site) and further upstream overlapping
the XyIR recognition sequence (Ps distal site). In the
latter case IHF recognition motifs were found well
conserved on both strands at nearly the same position
(between -140 bp and -152 bp on the upper and
between - 141 bp and - 153 bp on the lower strand).
Expression from Ps, either under inducing or noninducing
conditions, was, however, only slightly
influenced by the absence of IHF in an IHF-deficient
mutant and thus activation of Ps, like that of other
sigma54-dependent promoters which are rich in Ts,
does not absolutely require IHF protein.
This work
was supported by the Volkswagen Foundation Programme of
Partnership (1/65 166), the German-Spanish Cooperations
Programme 'Acciones Integradas' (AI91-24), the Fonds der
Chemischen Industrie (No. 163446) and by a grant from the
Comision Interministerial de Ciencia y Technologia (BT
091/0659). A.Holtel received a fellowship from the Spanish
Ministery of Education and, at an earlier stage, a short-term
EMBO fellowship (ASTF 5765).
Peer reviewed