Alterations in the Saccharomyces MAL-activator cause constitutivity but can be suppressed by intragenic mutations.
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.
Danzi
S E
SE
Department of Biology, Queens College and the Graduate School of CUNY, Flushing, NY 11367, USA.
Zhang
B
B
Michels
C A
CA
D000595:Amino Acid Sequence; D015971:Gene Expression Regulation, Enzymologic; D015966:Gene Expression Regulation, Fungal; D005800:Genes, Fungal; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000235:genetics*; D008969:Molecular Sequence Data; D009004:Monosaccharide Transport Proteins; D016297:Mutagenesis, Site-Directed; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics*; D016415:Sequence Alignment; D000520:alpha-Glucosidases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism
D026901:Membrane Transport Proteins; D009004:Monosaccharide Transport Proteins; D011993:Recombinant Fusion Proteins; C021534:maltose permease; D000520:alpha-Glucosidases