Functional Domain Analysis of the Saccharomyces MAL-activator

MAL63 of the MAL6 locus and its homologues at the other MAL loci encode transcription 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 Mal63 MAL-activator protein. Our results indicate that the sequence-specific DNA-binding domain of Mal63p is contained in residues 1-100; that residues 60-283 constitute a functional core region including the transactivation domain; that residues 251-299 are required to inhibit the activation function of Mal63p; and that the rest of the C-terminal region of the protein contains a maltose-responsive domain that acts to relieve the inhibitory effect on the activation function. Abundant overproduction of Mal63p does not overcome the negative regulation of MAL gene expression in the absence of maltose, suggesting that a titratable MAL-specific repressor similar to Gal80p is not involved in the negative regulation of the MAL-activator. A model for maltose-inducible autoregulation of the MAL-activator is presented.