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Title
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Sinorhizobium meliloti bluB is necessary for production of 5,6-dimethylbenzimidazole, the lower ligand of B12.
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Authors
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G.R.Campbell,
M.E.Taga,
K.Mistry,
J.Lloret,
P.J.Anderson,
J.R.Roth,
G.C.Walker.
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Ref.
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Proc Natl Acad Sci U S A, 2006,
103,
4634-4639.
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PubMed id
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Abstract
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An insight into a previously unknown step in B(12) biosynthesis was unexpectedly
obtained through our analysis of a mutant of the symbiotic nitrogen fixing
bacterium Sinorhizobium meliloti. This mutant was identified based on its
unusually bright fluorescence on plates containing the succinoglycan binding dye
calcofluor. The mutant contains a Tn5 insertion in a gene that has not been
characterized previously in S. meliloti. The closest known homolog is the bluB
gene of Rhodobacter capsulatus, which is implicated in the biosynthesis of B(12)
(cobalamin). The S. meliloti bluB mutant is unable to grow in minimal media and
fails to establish a symbiosis with alfalfa, and these defects can be rescued by
the addition of vitamin B(12) (cyanocobalamin) or the lower ligand of cobalamin,
5,6-dimethylbenzimidazole (DMB). Biochemical analysis demonstrated that the bluB
mutant does not produce cobalamin unless DMB is supplied. Sequence comparison
suggests that BluB is a member of the NADH/flavin mononucleotide (FMN)-dependent
nitroreductase family, and we propose that it is involved in the conversion of
FMN to DMB.
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