Characterization of Candida albicans ASH1 in Saccharomyces cerevisiae

Several fungi can undergo a dimorphic switch from yeast-like to hyphal or pseudohyphal forms in response to environmental cues. The Saccharomyces cerevisae GATA-type transcription factor Ash1p is required for diploid pseudohyphal differentiation during nitrogen starvation. In haploid cells, Ash1p is essential for the cell-type specific repression of the HO gene. We cloned CaAsh1, a putative homologue of Ash1p from the pathogen Candida albicans. Although the overall similarity of CaAsh1p and Ash1p is modest, both proteins show significant homology in their carboxy termini. Upon expression in budding yeast, CaASH1 mRNA is asymmetrically sorted during cell division, which is similar to the fate of ASH1 mRNA. Cell-specific CaASH1 mRNA localization results in an asymmetric CaAsh1 protein distribution and an accumulation of the protein in daughter cell nuclei. CaAsh1 is unable to repress HO expression in S. cerevisiae but can replace ScAsh1 function during pseudohyphal growth. This suggests a partial functional similarity of the two Ash1 proteins.