A STE12 homolog is required for mating but dispensable for filamentation in Candida lusitaniae

Candida lusitaniae is a dimorphic yeast that is emerging as an opportunisti c fungal pathogen. In contrast to Candida albicans, which is diploid and as exual, C. lusitaniae has been reported to have a sexual cycle. We have empl oyed genetic approaches to demonstrate that C. lusitaniae is haploid and ha s a sexual cycle involving mating between MATa and MAT alpha cell sunder nu trient deprivation conditions. By degenerate PCR, we identified a C. lusita niae homolog (Cls12) of the Ste12 transcription factor that regulates matin g, filamentation, and virulence in Saccharomyces cerevisiae, C. albicans, a nd Cryptococcus neoformans. Comparison of the CLS12 DNA and protein sequenc es to other STE12 homologs and transformation experiments with selectable m arkers from S. cerevisiae (URA3, KanMX, HphMX) and C. albicans (CaURA3) pro vide evidence that the CUG codon encodes serine instead of leucine in C. lu sitaniae, as is also the case in C. albicans. The C. lusitaniae CLS12 gene was disrupted by biolistic transformation and homologous recombination. C. lusitaniae cls12 mutant strains were sterile but had no defect in filamento us growth. Our findings reveal both conserved and divergent roles for the C . lusitaniae STE12 homolog in regulating differentiation of this emerging f ungal pathogen.