Cloning, sequencing and characterization of the alpha -aminoadipate reductase gene (LYS2) from Saccharomycopsis fibuligera

The gene putatively encoding -aminoadipate reductase (AAR) was isolated successfully by degenerate PCR and chromosome walking, based on cassette PCR methods, from the dimorphous yeast Saccharomycopsis fibuligera PD70 and was named SfLYS2. Sequence analysis revealed that it contained a putative open reading frame (ORF) of 4161 bp and encoded a polypeptide of 1386 amino acids. The deduced translation product shared an identity of 53% and 51% to the Lys2p homologues of Candida albicans and Saccharomyces cerevisiae, respectively. An atypical TATA box and a GCN4-box element were found in the 5-upstream region. Genomic Southern hybridization suggested the presence of a single locus of SfLYS2 in the S. fibuligera genome. Expression of the ORF of SfLYS2 in a lys2- strain of S. cerevisiae could functionally complement the lysine mutant of the S. cerevisiae strain. S. fibuligera could use lysine as the sole nitrogen source but its growth was inhibited on the -aminoadipate (AA) medium. Approximately 90% of the mutants of S. cerevisiae resistant to AA are lysine auxotrophs; in contrast all the mutants of S. fibuligera resistant to AA recovered in this work were not lysine auxotrophs. The GenBank Accession No. for SfLYS2 is DQ445618.