Summary: Vol. 171, No. 3JOURNAL OF BACTERIOLOGY, Mar. 1989, p. 1673-1682
Copyright © 1989, American Society for Microbiology
Rhizobium meliloti 1021 Has Three Differentially Regulated Loci
Involved in Glutamine Biosynthesis, None of Which Is Essential for
Symbiotic Nitrogen Fixationt
FRANS J. DE BRUIJN,l.2* SILVIA ROSSBACH,'t MARIA SCHNEIDER,' PASCAL RATET,1 SABINE MESSMER,'
WYNNE W. SZETO,2§ FREDERICK M. AUSUBEL,2 AND JEFF SCHELL'
Max-Planck-Institut fur Zuchtungsforschung, D-5000 Cologne 30, Federal Republic of Germany,l*
and Department of Genetics, Harvard Medical School, and Department ofMolecular Biology,
Massachusetts General Hospital, Boston, Massachusetts 021142
Received 16 September 1988/Accepted 7 December 1988
We have cloned and characterized three distinct Rhizobium meliloti loci involved in glutamine biosynthesis
(ginA, glnlI, and glnT). The ginA locus shares DNA homology with the glnA gene of Klebsiella pneumoniae,
encodes a 55,000-dalton monomer subunit of the heat-stable glutamine synthetase (GS) protein (GSI), and
complemented an Escherichia coli glnA mutation. The glnlI locus shares DNA homology with the glnll gene of
Bradyrhizobiumjaponicum and encodes a 36,000-dalton monomer subunit of the heat-labile GS protein (GSII).
The glnT locus shares no DNA homology with either the ginA or ginlI gene and complemented a glnA E. coli
strain. The ginT locus codes for an operon encoding polypeptides of 57,000, 48,000, 35,000, 29,000, and 28,000
daltons. ginA and glnlI insertion mutants were glutamine prototrophs, lacked the respective GS form (GSI or