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J. Bacteriol., Nov 1997, 7103-7110, Vol 179, No. 22
HG Wiggerich, B Klauke, R Koplin, UB Priefer and A Puhler
The nucleotide sequence of a 3.6-kb HindIII-SmaI DNA fragment of
Xanthomonas campestris pv. campestris revealed four open reading frames
which, based on sequence homologies, were designated tonB, exbB, exbD1, and
exbD2. Analysis of translational fusions to alkaline phosphatase and
beta-galactosidase confirmed that the TonB, ExbB, ExbD1, and ExbD2 proteins
are anchored in the cytoplasmic membrane. The TonB protein of X. campestris
pv. campestris lacks the conserved (Glu-Pro)n and (Lys- Pro)m repeats but
harbors a 13-fold repeat of proline residues. By mutational analysis, the
tonB, exbB, and exbD1 genes were shown to be essential for ferric iron
import in X. campestris pv. campestris. In contrast, the exbD2 gene is not
involved in the uptake of ferric iron.
Copyright © 1997, American Society for Microbiology
Unusual structure of the tonB-exb DNA region of Xanthomonas campestris pv. campestris: tonB, exbB, and exbD1 are essential for ferric iron uptake, but exbD2 is not
Lehrstuhl fur Genetik, Fakultat fur Biologie, Universitat Bielefeld, Germany.
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