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J. Bacteriol., 06 1996, 3212-3220, Vol 178, No. 11
M Cieslewicz and E Vimr
The kps locus for biosynthesis of the capsular polysialic acid virulence
factor in Escherichia coli K1 contains at least two convergently
transcribed operons, designated region 1 and regions 2 plus 3. On the basis
of DNA sequence analysis, kpsF appeared to be a good candidate for the
first gene of region 1 (M. J. Cieslewicz, S. M. Steenbergen, and E. R.
Vimr, J. Bacteriol. 175:8018-8023, 1993). A preliminary indication that
kpsF is required for capsule production is the capsule-negative phenotype
of an aph T insertion in the chromosomal copy of kpsF. The present
communication describes the isolation and phenotypic characterization of
this mutant. Although transcription through kpsF was required for capsule
production, complementation analysis failed to indicate a clear requirement
for the KpsF polypeptide. However, since E. coli contains at least two
other open reading frames that could code for homologs of KpsF, the
apparent dispensability of KpsF remains provisional. DNA sequence analysis
of 1,100 bp upstream from the kpsF translational start site did not reveal
any open reading frames longer than 174 nucleotides, consistent with kpsF
being the first gene of region 1. Since kpsF appeared to be the first gene
of a region whose gene products are required for polysialic acid transport
and because capsule production is known to be thermoregulated, primer
extension analyses were carried out with total RNA isolated from cells
grown at permissive (37 degrees C) and nonpermissive (20 degrees C)
temperatures. The results revealed a potentially complex kpsF promoter-like
region that was transcriptionally silent at the nonpermissive temperature,
suggesting that thermoregulation of region 1 may be exerted through
variations in kpsF expression. Additional evidence supporting this
conclusion was obtained by demonstrating the effects of temperature on
expression of the gene kpsE, immediately downstream of kpsF.
Chloramphenicol acetyltransferase assays were carried out with constructs
containing the kpsF 5' untranslated region fused to a promoterless cat
cassette, providing further evidence that kpsF is thermoregulated. Although
the function of KpsF is unclear, primary structure analysis indicated two
motifs commonly observed in regulatory proteins and homology with
glucosamine synthase from Rhizobium meliloti.
Copyright © 1996, American Society for Microbiology
Thermoregulation of kpsF, the first region 1 gene in the kps locus for polysialic acid biosynthesis in Escherichia coli K1
Department of Veterinary Pathobiology, University of Illinois at Urbana- Champaign 61801, USA.
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