Alterations in the Saccharomyces MAL-activator cause constitutivity but can be suppressed by intragenic mutations

Curr Genet. 2000 Dec;38(5):233-40. doi: 10.1007/s002940000161.


The Saccharomyces MAL-activator regulates the maltose-inducible expression of the MAL structural genes encoding maltose permease and maltase. Constitutive MAL-activator mutant alleles of two types were identified. The first were truncation mutations deleting C-terminal residues 283-470 and the second contained a large number of alterations compared to inducible alleles scattered throughout the C-terminal 200 residues. We used site-directed in vitro mutagenesis of the inducible MAL63 and MAL63/23 genes to identify the residues responsible for the negative regulatory function of the C-terminal domain. Intragenic suppressors that restored the inducible phenotype to the constitutive mutants were identified at closely linked and more distant sites within the MAL-activator protein. MAL63/mal64 fusions of the truncated mutants suggest that residues in the N-terminal 100 residues containing the DNA-binding domain also modulate basal expression. Moreover, a transcription activator protein consisting of LexA(1-87)-Gal4(768-881)-Mal63(200-470) allowed constitutive reporter gene expression, suggesting that the C-terminal regulatory domain is not sufficient for maltose-inducible control of this heterologous activation domain. These results suggest that complex and very specific intramolecular protein-protein interactions regulate the MAL-activator.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Gene Expression Regulation, Enzymologic
  • Gene Expression Regulation, Fungal*
  • Genes, Fungal
  • Membrane Transport Proteins / chemistry
  • Membrane Transport Proteins / genetics*
  • Molecular Sequence Data
  • Monosaccharide Transport Proteins
  • Mutagenesis, Site-Directed
  • Recombinant Fusion Proteins / chemistry
  • Recombinant Fusion Proteins / metabolism
  • Saccharomyces cerevisiae / enzymology*
  • Saccharomyces cerevisiae / genetics*
  • Sequence Alignment
  • alpha-Glucosidases / chemistry
  • alpha-Glucosidases / genetics*
  • alpha-Glucosidases / metabolism


  • Membrane Transport Proteins
  • Monosaccharide Transport Proteins
  • Recombinant Fusion Proteins
  • maltose permease
  • alpha-Glucosidases