Genetic regulation of isocitrate lyase activity in Aspergillus nidulans

Glucose-induced inactivation of isocitrate lyase in Aspergillus nidulans

The existence of a second mechanism of catabolite control of isocitrate lyase of Aspergillus nidulans, in addition to the carbon catabolite repression phenomenon recently reported was analysed. Isocitrate lyase was rapidly and specifically inactivated by glucose. The inactivation was irreversible at all stages in the presence of cycloheximide, showing that reactivation depends on de novo protein synthesis. In addition, analysis of glucose-induced inactivation of isocitrate lyase in a creAd-30 strain showed that the creA gene is not involved in this process.

Genetic analysis of the gene ICL1 of the yeast Yarrowia lipolytica

The gene ICL1 codes for the tetrameric enzyme isocitrate lyase of Y. lipolytica. Twenty icl1- alleles have been analysed for their reversion frequency, their interallelic complementation pattern, and the position of the corresponding mutation site on the fine structure map of the gene ICL1. One intragenic temperature-sensitive revertant of the allele icl1D-39 was isolated, which expressed a thermolabile enzyme. In spite of the fact that nonsense mutations have been detected, the direction of transcription of the gene ICL1 was inferred from the localization of a linked cis-dominant regulatory mutation site. The size of the mitotic map of this gene suggests that recombination frequency in Y. lipolytica is lower than in Saccharomyces cerevisiae.