Two mutants carrying different deletions of the coding sequence of , Ã1, which encodes a protein lacking the last 26 C-terminal amino acids, and Ã2, which completely lacks the coding region, were analysed for derepression of glucose-repressible maltose, galactose, raffinose and ethanol utilization pathways in response to glucose limitation. The role of the gene product in the regulation of carbon catabolite repressible enzymes maltase, invertase, alcohol dehydrogenase, NAD-dependent glutamate dehydrogenase (NAD-GDH) and L-lactate:ferricytochrome-c oxidoreductase (L-LCR) was also analysed. The gene product is required for the rapid glucose derepression of all above-mentioned carbon source utilization pathways and of all the enzymes except for L-LCR. NAD-GDH is regulated by in the opposite way and, in fact, this enzyme was released at higher levels in both mutants than in the wild-type strain. Therefore, the product of appears to be involved in positive and negative regulation. Both deletions result in growth and catalytic defects; in some cases partial modification of the gene product yielded more dramatic effects than its complete absence. Moreover, evidence is provided that the gene product regulates galactose- and maltose-inducible genes at the transcriptional level and is a positive regulator of maltase, maltose permease and galactose permease gene expression.


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