Nucleotide sequence of an alfalfa glutamine synthetase gene

Abstract

One of the members of the small gene family encoding glutamine synthetase in alfalfa (Medicago sativa L.) has been cloned and its nucleotide sequence determined. Approximately full length cDNAs corresponding to the gene have also been cloned and their sequences determined. The gene is about 4 kb long, and consists of twelve exons (size range 37 to 159 bp) and eleven introns (size range 90 to 715 bp). The messenger RNA contains a 120 nucleotide 5′-untranslated region, a 1,071 nucleotide coding region, and a 210 nucleotide 3′-untranslated region. Several eukaryotic consensus transcription and processing signals are present in this plant gene: (1) a TATA box (TATAAATA) 25 bp 5′ to the putative transcription start site; (2) a potential polyadenylation signal (AATAATAA) 20 bp 5′ to the polyadenylation site; and (3) the terminal dinucleotides of the introns (5′-GT...AG-3′). Also the dinucleotide, CpG, is significantly underrepresented throughout the gene. The derived amino acid sequence predicts a relatively hydrophilic protein with a molecular weight of 39,215. Several regions of amino acid homology are apparent when this sequence is compared to the Anabaena and Chinese hamster glutamine synthetase sequences. Using data derived from the gene structure, the minimum size of a glutamine synthetase gene amplification unit in an l-phosphinothricin resistant alfalfa tissue culture line has been determined to be 35 kb.