The MAL locus of Hansenula polymorpha is organized similarly to respective gene clusters of other yeasts and hides a divergent promoter with a biotechnological potential.
Tiina Alamäe, Katrin Viigand, Birgit Rätsep, Kersti Tammus
Department of Genetics, University of Tartu, 23 Riia Str, Tartu, 51010, Estonia
Methylotrophic yeast Hansenula polymorpha has no invertase and it uses maltase to grow on maltose and sucrose. Genomic clones of H. polymorpha show that the maltase gene is clustered with genes homologous to yeast maltose permeases and MAL activators, respectively, constituting the MAL locus. Divergently positioned maltase and maltose permease genes share the intergenic region. Similar genomic organization of the maltase and maltose permease genes is found in baker's yeast, Kluyveromyces lactis, Torulaspora delbrueckii and Candida albicans. Reporter gene assay was applied to study expression from the respective divergent promoter region of H. polymorpha. Expression from the promoter was induced by maltose and sucrose, and repressed by glucose in both directions. Thus, the promoter can be applied for regulated coexpression of two different proteins of interest in H. polymorpha. The maltose permease gene of the H. polymorpha MAL locus was cloned and sequenced. The protein (582 amino acids) deduced from the gene has 41-51% identity to yeast maltose permeases and reveals eleven transmembrane domains. The maltose permease from C. albicans is the closest homologue of the H. polymorpha permease showing 51% of identity. The closest homologue (58% identity) of the H. polymorpha maltase protein is also the maltase from C. albicans. Thus, the MAL loci of these two yeasts may have common evolutionary origin.