The hexokinase 2 protein participates in regulatory DNA‐protein complexes necessary for glucose repression of the SUC2 gene in Saccharomyces cerevisiae

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Abstract
The HXK2 gene plays an important role in glucose repression in the yeast Saccharomyces cerevisiae. Recently we have described that the HXK2 gene product, isoenzyme 2 of hexokinase, is located both in the nucleus and in the cytoplasm of S. cerevisiae cells. In this work we used deletion analysis to identify the essential part of the protein‐mediating nuclear localisation. Determinations of fructose‐kinase activity and immunoblot analysis using anti‐Hxk2 antibodies in isolated nuclei, together with observations of the fluorescence distribution of Hxk2‐GFP fusion protein in cells transformed with an HXK2::gfp mutant gene, indicated that the decapeptide KKPQARKGSM, located between amino acid residues 7 and 16 of hexokinase 2, is important for nuclear localisation of the protein. Further experimental evidence, measuring invertase activity in wild‐type and mutant cells expressing a truncated version of the Hxk2 protein unable to enter the nucleus, shows that a nuclear localisation of Hxk2 is necessary for glucose repression signalling of the SUC2 gene. Furthermore, we demonstrate using gel mobility shift analysis that Hxk2 participates in DNA‐protein complexes with cis‐acting regulatory elements of the SUC2 gene promoter.