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Rhizobium astragali 159 has two nodD genes that differ in primary structure and function

Abstract

Rhizobium astragali strain 159 has two homologs of the nodulation regulatory gene, nodD. These homologs, nodD1 and nodD2, are located upstream of the nodBC gene cluster and the nodA gene respectively. The two predicted NodD proteins, as derived from the nucleotide sequence of the respective genes, shared 69% identical amino acid residues at corresponding positions and had the structural characteristics known for NodD proteins from other rhizolia: a highly conserved sequence containing the helix-turn-helix motif for DNA binding. However, compared with NodD1 protein, NodD2 had 67 amino acid deletions in the N-terminal region. Measurements of #beta#0galactosidase activities revealed that nodD1-lacZ and nodD2-lacZ fusion were expressed constitutively in R. astragali 159. The predicted NodD1 could activate the expression of R. meliloti nodC-lacZ fusion in the presence of Astragalus sinicus seed exudate, but NodD2 could not.

Key words: Rhizobium astragali;nodD gene;Nucleotide sequence;Functional analysis

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Citing This Article：

. Rhizobium astragali 159 has two nodD genes that differ in primary structure and function. Acta Physiol Sin 1998; 50 (1): (in Chinese with English abstract).