The cold-inducible icl gene encoding thermolabile isocitrate lyase of a psychrophilic bacterium, Colwellia marisa

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The gene encoding isocitrate lyase (ICL; EC 4.1.3.1) of a psychrophilic bacterium, Colwellia maris, was cloned and sequenced. The ORF of the gene (icl) was 1584 bp long, and the predicted gene product consisted of 528 aa (molecular mass 58150 Da) and showed low homology with the corresponding enzymes from other organisms. The analyses of amino acid content and primary structure of the C. maris ICL suggested that it possessed many features of a cold-adapted enzyme. Primer extension and Northern blot analyses revealed that two species of the icl mRNAs with differential lengths of 5'-untranslated regions (TS1 and TS2) were present, of which the 5' end (TS1 and TS2 sites) were G and A, located at 130 and 39 bases upstream of the translation start codon, respectively. The levels of TS1 and TS2 mRNAs were increased by both acetate and low temperature. The induction of icl expression by low temperature took place in the C. maris cells grown on succinate as the carbon source but not acetate. Furthermore, a similar manner of inductions was also found in the levels of the translation and the enzyme activity in cell-free extract. These results suggest that the icl gene, encoding thermolabile isocitrate lyase, of C. maris is important for acetate utilization and cold adaptation.
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