Molecular characterization of guanosine kinase gene from a facultative alkalophile, Exiguobacterium aurantiacum ATCC 35652.

Guanosine kinase activity was identified in an alkalophile, Exiguobacterium aurantiacum ATCC 35652, and the gsk gene encoding it was isolated as a homologous fragment of the Brevibacterium acetylicum gsk. The cloned chromosomal fragment contained an open reading frame which encodes a polypeptide of 308 amino acids with a molecular mass of 33349 Da. The Ex. aurantiacum Gsk shows strong sequence similarity to B. acetylicum Gsk, but possesses five additional amino acids at the C-terminus. An Mr 39200 protein synthesized in Escherichia coli harboring plasmids carrying Ex. aurantiacum gsk was purified and characterized. A 0.9 kb transcript revealed by Northern blot analysis and the presence of a factor-independent terminator structure suggest that Ex. aurantiacum gsk is monocistronic, although B. acetylicum gsk has been shown to be bicistronic. The striking alterations in the 3'-untranslated region resulted in a different gene organization.