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J. Bacteriol., Apr 1995, 1734-1741, Vol 177, No. 7
J Dworkin, MK Tummuru and MJ Blaser
Campylobacter fetus cells can produce multiple S-layer proteins ranging
from 97 to 149 kDa, with a single form predominating in cultured cells. We
have cloned, sequenced, and expressed in Escherichia coli a sapA homolog,
sapA2, which encodes a full-length 1,109-amino-acid (112-kDa) S-layer
protein. Comparison with the two previously cloned sapA homologs has
demonstrated two regions of identity, approximately 70 bp before the open
reading frame (ORF) and proceeding 550 bp into the ORF and immediately
downstream of the ORF. The entire genome contains eight copies of each of
these conserved regions. Southern analyses has demonstrated that sapA2
existed as a complete copy within the genome in all strains examined,
although Northern (RNA) analysis has demonstrated that sapA2 was not
expressed in the C. fetus strain from which it was cloned. Further Southern
analyses revealed increasing sapA diversity as probes increasingly 3'
within the ORF were used. Pulsed-field gel electrophoresis and then
Southern blotting with the conserved N- terminal region of the sapA
homologs as a probe showed that these genes were tightly clustered on the
chromosome. Deletion mutagenesis revealed that the S-layer protein bound
serospecifically to the C. fetus lipopolysaccharide via its conserved
N-terminal region. These data indicated that the S-layer proteins shared
functional activity in the conserved N terminus but diverged in a
semiconservative manner for the remainder of the molecule. Variation in
S-layer protein expression may involve rearrangement of complete gene
copies from a single large locus containing multiple sapA homologs.
Copyright © 1995, American Society for Microbiology
A lipopolysaccharide-binding domain of the Campylobacter fetus S-layer protein resides within the conserved N terminus of a family of silent and divergent homologs
Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee 37232.
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