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J Bacteriol. 1992 June; 174(11): 3667-3675

research-article

Mutational analysis reveals functional similarity between NARX, a nitrate sensor in Escherichia coli K-12, and the methyl-accepting chemotaxis proteins.

L A Collins, S M Egan and V Stewart

Section of Genetics, Cornell University, Ithaca, New York 14853-8101.

ABSTRACT

During anaerobic growth, nitrate induces synthesis of the anaerobic respiratory enzymes formate dehydrogenase-N and nitrate reductase. This induction is mediated by a transcription activator, the narL gene product. The narX gene product may be involved in sensing nitrate and phosphorylating NARL. We isolated narX mutants, designated narX*, that caused nitrate-independent expression of the formate dehydrogenase-N and nitrate reductase structural genes. We used lambda narX specialized transducing phage to genetically analyze these lesions in single copy. Two previously isolated narX* mutations, narX32 and narX71, were also constructed by site-specific mutagenesis. We found that each of these alleles caused nitrate-independent synthesis of formate dehydrogenase-N and nitrate reductase, and each was recessive to narX+. The narX* mutations lie in a region of similarity with the methyl-accepting chemotaxis protein Tsr. We suggest that the narX* proteins have lost a transmembrane signalling function such that phosphoprotein phosphatase activity is reduced relative to protein kinase activity.

J Bacteriol. 1992 June; 174(11): 3667-3675




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