We analyzed a cDNA clone encoding cytosolic glutamine synthetase, EuNOD-GS1, isolated from a root nodule cDNA library of Elaeagnus umbellata. This clone has an insert size of 1359 bp and encodes a protein for 355 amino-acid residues, with a molecular weight of 39.2 kDa. Its expression is slightly higher in the root nodules than in the leaves or uninfected roots. Analysis of the deduced amino acid sequences and phylogeny revealed that EuNOD-GS1 is clustered with cytosolic GS-a isoenzymes. Therefore, based on this and previous results, we propose that the main physiological role of EuNOD-GS1 is the assimilation of ammonia from secondary and, in part, primary sources.