Functional domain analysis of the Saccharomyces MAL-activator

MAL63 of the MAL6 locus and its homologues at the other MAL loci encode tra nscription activators required for the maltose-inducible expression of the MAL structural genes. We carried out a deletion analysis of LexA-MAL63 gene fusions to localize the functional domains of the Ma163 MAL-activator prot ein. Our results indicate that the sequence-specific DNA-binding domain of Ma163p is contained in residues 1-100; that residues 60-283 constitute a fu nctional core region including the transactivation domain; that residues 25 1-299 are required to inhibit the activation function of Ma163p; and that t he rest of the C-terminal region of the protein contains a maltose-responsi ve domain that acts to relieve the inhibitory effect on the activation func tion. Abundant overproduction of Ma163p does not overcome the negative regu lation of MAL gene expression in the absence of maltose, suggesting that a titratable MAL-specific repressor similar to Ga180p is not involved in the negative regulation of the MAL-activator. A model for maltose-inducible aut oregulation of the MAL-activator is presented.