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Characterization of the Overlapping Promoters of nolB and nolW, Two Soybean Cultivar Specificity Genes from Rhizobium fredii Strain USDA257

January 1997 , Volume 10 , Number  1
Pages  138 - 141

Jun Gu , Pedro A. Balatti , Hari B. Krishnan , and Steven G. Pueppke

Department of Plant Pathology, University of Missouri, Columbia, MO 65211 U.S.A.

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Accepted 30 October 1996.

The transcripts of nolW and nolB, two divergently oriented cultivar specificity genes of Rhizobium fredii strain USDA257, are known to be initiated 14 bp apart from promoters that face one another. We show here that expression of nolB is dependent both on induction with flavonoid signals and on the regulatory gene, nodD1. Expression of nolW is constitutive and independent of flavonoids and nodD1. Normal expression of nolB is retained with a promoter that extends only 61 bp upstream of the transcript start site, but it is lost if an additional 24 bp are removed. Substantial expression of nolW is retained with a promoter that contains only 34 bp of DNA upstream from the transcript initiation site. The dual control region for the two genes is thus only about 109 bp in length.

© 1997 The American Phytopathological Society