STRUCTURE AND REGULATION OF THE ISOCITRATE LYASE GENE ICL1 FROM THE YEAST SACCHAROMYCES-CEREVISIAE

The ICL1 gene encoding the isocitrate lyase from Saccharomyces cerevis iae was cloned and sequenced. A reading frame of 557 amino acids showi ng significant similarity to isocitrate lyases from seven other specie s could be identified. Construction of icl1 null mutants led to growth defects on C2 carbon sources while utilization of sugars or C3 substr ates remained unaffected. Using an ICL1-lacZ fusion integrated at the ICL1 locus, a more than 200-fold induction of beta-galactosidase activ ity was observed after growth on ethanol when compared with glucose-re pressed conditions. A preliminary analysis of the ICL1 upstream region identified a 364-bp fragment necessary and sufficient for this regula tory phenotype. Sequence motifs also present in the upstream regions o f co-regulated genes were found within this region.