ISOLATION OF CASLN1 AND CANIK1, THE GENES FOR OSMOSENSING HISTIDINE KINASE HOMOLOGS, FROM THE PATHOGENIC FUNGUS CANDIDA-ALBICANS

Recent studies have revealed that fungi possess a mechanism similar to bacterial two-component systems to respond to extracellular changes i n osmolarity, In Saccharomyces cerevisiae, Sln1p contains both histidi ne kinase and receiver (response regulator) domains and acts as an osm osensor protein that regulates the downstream HOG1 MAP kinase cascade. SLN1 of Candida albicans was functionally cloned using an S. cerevisi ae strain in which SLN1 expression was conditionally suppressed. Delet ion analysis of the cloned gene demonstrated that the receiver domain of C. albicans Sln1p was not necessary to rescue SLN1-deficient S. cer evisiae strains. Unlike S. cerevisiae, a null mutation of C. albicans SLN1 was viable under regular and high osmotic conditions, but it caus ed a slight growth retardation at high osmolarity. Southern blotting w ith C. albicans SLN1 revealed the presence of related genes, one of wh ich is highly homologous to the NIK1 gene of Neurospora crassa. Thus, C. albicans harbours both SLN1- and NIK1-type histidine kinases.