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J. Bacteriol., Jul 1997, 4607-4615, Vol 179, No. 14
HL Lumppio, NV Shenvi, RP Garg, AO Summers and DM Kurtz Jr
Rubrerythrin is a nonheme iron protein of unknown function isolated from
Desulfovibrio vulgaris (Hildenborough). We have sequenced a 3.3- kbp Sal1
fragment of D. vulgaris chromosomal DNA containing the rubrerythrin gene,
rbr, identified additional open reading frames (ORFs) adjacent to rbr, and
shown that these ORFs are part of a transcriptional unit containing rbr.
One ORF, designated fur, lies just upstream of rbr and encodes a
128-amino-acid-residue protein which shows homology to Fur (ferric uptake
regulatory) proteins from other purple bacteria. The other ORF, designated
rdl, lies just downstream of rbr and encodes a 74-residue protein with
significant sequence homology to rubredoxins but with a different number
and spacing of cysteine residues. Overexpression of rdl in Escherichia coli
yielded a protein, Rdl, which has spectroscopic properties and iron content
consistent with one Fe3+(SCys)4 site per polypeptide but is clearly
distinct from both rubrerythrin and a related protein, nigerythrin.
Northern analysis indicated that fur, rbr, and rdl were each present on a
transcript of 1.3 kb; i.e., these three genes are cotranscribed. Because D.
vulgaris nigerythrin appears to be closely related to rubrerythrin, and its
function is also unknown, we cloned and sequenced the gene encoding
nigerythrin, ngr. The amino acid sequence of nigerythrin is 33% identical
to that of rubrerythrin, and all residues which furnish iron ligands to
both the FeS4 and diiron-oxo sites in rubrerythrin are conserved in
nigerythrin. Despite the close resemblance of these two proteins, ngr was
found to be no closer than 7 kb to rbr on the D. vulgaris chromosome, and
Northern analysis showed that, in contrast to rbr, ngr is not cotranscribed
with other genes. Possible redox-linked functions for rubrerythrin and
nigerythrin in iron homeostasis are proposed.
Copyright © 1997, American Society for Microbiology
A rubrerythrin operon and nigerythrin gene in Desulfovibrio vulgaris (Hildenborough)
Department of Microbiology and Center for Metalloenzyme Studies, University of Georgia, Athens 30602, USA.
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