J Bacteriol, June 1998, p. 3260-3264, Vol. 180, No. 12
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Department of Plant Pathology, College of Agriculture, University of Arizona, Tucson, Arizona 85721
Received 20 January 1998/Accepted 7 April 1998
To determine whether in Azotobacter vinelandii the PII protein influences the regulation of nif gene expression in response to fluxes in the ammonium supply, the gene encoding PII was isolated and characterized. Its deduced translation product was highly similar to PII proteins from other organisms, with the greatest degree of relatedness being exhibited to the Escherichia coli glnK gene product. A gene designated amtB was found downstream of and was cotranscribed with glnK as in E. coli. The AmtB protein is similar to functionally characterized ammonium transport proteins from a few other eukaryotes and one other prokaryote. glnK and amtB comprise an operon. Attempts to isolate a stable glnK mutant strain were unsuccessful, suggesting that glnK, like glnA, is an essential gene in A. vinelandii. amtB mutants were isolated, and although growth on limiting amounts of ammonium was similar in the mutant and wild-type strains, the mutants were unable to transport [14C]methylammonium.
Present address: Gentechnologie/Mikrobiologie, Fakultät
für Biologie, Universität Bielefeld, 33501 Bielefeld,
Germany.
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