SUMMARY: The structural gene () encoding the glutamine synthetase (GS) of the extremely thermophilic eubacterium has been cloned on a 6·0 kb III DNA fragment. Sequencing of the region containing the gene (1444 bp) showed an ORF encoding a polypeptide (439 residues) with an estimated mass of 50088 Da, which shared significant homology with the GSI sequences of other Bacteria () and Archaea (). The gene was expressed in , as shown by the ability to complement a lesion in the glutamine-auxotrophic strain ET8051. The recombinant GS has been partially characterized with respect to the temperature dependence of enzyme activity, molecular mass and mode of regulation. The molecular mass of the GS (590000 Da), estimated by gel filtration, was compatible with a dodecameric composition for the holoenzyme, as expected for a glutamine synthetase of the GSI type. Comparison of the amino acid sequence of GS with those from thermophilic and mesophilic micro-organisms failed to detect any obvious features directly related to thermal stability.


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