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J. Bacteriol., Apr 1996, 1782-1787, Vol 178, No. 7
MJ Barnett, BG Rushing, RF Fisher and SR Long
In Rhizobium meliloti the syrM regulatory gene positively controls nod D3
and syrA, and nodD3 positively controls syrM and nod regulon genes such as
nodABC, syrM and nodD3 are divergently transcribed and are separated by
approximately 2.8 kb of DNA. The 885-bp SphI DNA fragment between syrM and
nodD3 was subcloned and sequenced. Analysis of this intergenic region
showed two open reading frames similar to those found in insertion elements
of the IS3 family. We determined transcription initiation sites for both
syrM and nodD3 using primer extension. The syrM transcription initiation
site is 499 bp upstream of the syrM protein-coding region and downstream of
a nod box which shows several differences from the R. meliloti nod box
consensus sequence. We demonstrated binding of NodD3 to DNA containing the
syrM nod box. The nodD3 start site maps 659 bp upstream of the nodD3
translation initiation site. A putative SyrM binding site was identified
upstream of the nodD3 start site on the basis of sequence similarity to the
upstream region of syrA, another locus regulated by SyrM.
Copyright © 1996, American Society for Microbiology
Transcription start sites for syrM and nodD3 flank an insertion sequence relic in Rhizobium meliloti
Department of Biological Sciences, Stanford University, California 94305, USA.
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