A. H. F.
A. W. B.
1School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, U. K.; 2School of Animal and Microbial Science, University of Reading, Reading RG6 6AJ, U.K.;3John Innes Centre, Colney Lane, Norwich NR4 7UH, U.K.
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Accepted 1 October 2001.
An operon with homology to the dppABCDF genes required to transport dipeptides in bacteria was identified in the N2-fixing symbiont, Rhizobium leguminosarum. As in other bacteria, dpp mutants were severely affected in the import of δ-aminolevulinic acid (ALA), a heme precursor. ALA uptake was antagonized by adding dipeptides, indicating that these two classes of molecule share the same transporter. Mutations in dppABCDF did not affect symbiotic N2 fixation on peas, suggesting that the ALA needed for heme synthesis is not supplied by the plant or that another uptake system functions in the bacteroids. The dppABCDF operon of R. leguminosarum resembles that in other bacteria, with a gap between dppA and dppB containing inverted repeats that may stabilize mRNA and may explain why transcription of dppA alone was higher than that of dppBCDF. The dppABCDF promoter was mapped and is most likely recognized by σ70.
© 2002 The American Phytopathological Society