CLONING OF THE ISOCITRATE LYASE GENE (ICL1) FROM YARROWIA-LIPOLYTICA AND CHARACTERIZATION OF THE DEDUCED PROTEIN

The ICL1 gene encoding isocitrate lyase was cloned from the dimorphic fungus Yarrowia lipolytica by complementation of a mutation (acuA 3) in the structural gene of isocitrate lyase of Escherichia coli. The open reading frame of ICL1 is 1668 bp long and contains no introns in contrast to currently sequenced genes from other filamentous fungi. The ICL1 gene encodes a deduced protein of 555 amino acids with a molecular weight of 62 kDa, which fits the observed size of the purified monomer of isocitrate lyase from Y lipolytica. Comparison of the protein sequence with those of known pro- and eukaryotic isocitrate lyases revealed a high degree of homology among these enzymes. The isocitrate lyase of Y lipolytica is more similar to those from Candida tropicalis and filamentous fungi than to Sacharomyces cerevisiae. This enzyme of Y lipolytica has the putative glyoxysomal targeting signal S-K-L at the carboxy-terminus. It contains a partial repeat which is typical for eukaryotic isocitrate lyases but which is absent from the E. coli enzyme. Surprisingly, deletion of the ICL1 gene from the genome not only inhibits the utilization of acetate, ethanol, and fatty acids, but also reduces the growth rate on glucose.