SEQUENCE CONSERVATION IN THE SACCHAROMYCES AND KLUVEROMYCES GAL11 TRANSCRIPTION ACTIVATORS 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 structure-function relationships of GAL11 we cloned and sequenced a homologue from the yeast Kluyveromyces lactis, Kl-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 Kl-GAL11 the alanines in such runs are replaced by proline and other residues. The primary sequence similarity is reflected in functional similarity since a gal11 mutation in K.lactis creates phenotypes similar to those seen previously in gall 1-defective S.cerevisiae. In addition, KI-GAL11 complements a gall 1-defect in S.cerevisiae by partially restoring induction of GAL1 expression, growth on nonfermentable carbon sources, and phosphorylation of GAL4.