Sequence conservation in the Saccharomyces and Kluveromyces GAL11 transcription acvivators suggests functional domains

Efficient transcription of many Saccharomyces cerevisiae genes requires the GAL11 Protein. GAL11 belongs to a class of transcription activator that lacks a DNA-binding domain. Such proteins are thought to activate specific genes by complexing with DNA-bound proteins. To begin to understand the domain tructurefunction relationships of GAL11 we cloned and sequenced a homologue from the yeast Kluyveromyces lactis, KI-GAL11. The two predicted GAL11 proteins show high overall amino acid conservation and an unusual amino acid composition including 18% glutamine, 10% asparagine (S.cerevisiae) or 7% (K.lactis), and 8% proline (K.lactis) or 5% (S.cerevisiae) residues. Both proteins have runs of pure glutamines. Sc-GAL11 has glutamine-alanine runs but in KI-GAL11 the alanines in such runs are replaced by proline and other residues. The primary sequence similarity is reflected in functional similarity since a gall 1 mutation in K.lactis creates phenotypes similar to those seen previously in gall 7-defective S.cerevisiae. In addition, KI-GAL11 complements a ga/f f-defect in S.cerevisiae by partially restoring induction of GAL1 expression, growth on nonfermentable carbon sources, andphosphorylation of GAL4.