Summary auto-generated
This study describes the isolation and characterization of CaSSD1, a homologue of the Saccharomyces cerevisiae SSD1 gene, from the human pathogen Candida albicans. The researchers identified CaSSD1 by screening a C. albicans genomic library for clones capable of rescuing temperature-sensitive swi4 mutations in yeast strains lacking functional SSD1. The CaSSD1 gene encodes a 1262 amino acid protein showing 47% identity to S. cerevisiae SSD1 and significant homology to related fungal proteins. Domain analysis revealed that conserved regions are essential for function, with deletion of any conserved domain abolishing complementation ability. CaSSD1 transcription remains constitutive throughout the mitotic cell cycle, consistent with a housekeeping role in cell growth. Like its yeast counterpart, CaSSD1 suppresses temperature-sensitive mutations in genes encoding protein phosphatase 2A catalytic subunits, indicating functional conservation of this suppressor mechanism across fungal species. The findings suggest that cell cycle regulatory mechanisms are partially conserved between S. cerevisiae and C. albicans.
Key findings
- CaSSD1 from C. albicans shares 47% amino acid identity with S. cerevisiae SSD1 and can functionally suppress swi4 temperature-sensitive mutations in yeast
- Conserved domains within CaSSD1 are essential for function, with deletion of any conserved region eliminating complementation ability
- CaSSD1 expression is constitutive throughout the mitotic cell cycle, suggesting a role in general cell growth rather than cell cycle-specific regulation
- CaSSD1 suppresses temperature-sensitive mutations in genes encoding protein phosphatase 2A catalytic subunits, demonstrating functional conservation of this suppressor mechanism across fungal species
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Abstract
The SSD1 gene of Saccharomyces encodes a 160 kDa cytoplasmic protein that can suppress mutations in a number of other genes. A functional homologue of SSD1 from the human pathogen Candida albicans was isolated on the basis of its ability to restore viability at the restrictive temperature in a Saccharomyces cerevisiae swi4 ssd1-d strain. The C. albicans gene, designated CaSSD1, encodes a 1262 aa protein which has 47% identity overall to S. cerevisiae SSD1 as well as significant identity to Schizosaccharomyces pombe dis3 and sts5 products. It is shown that CaSSD1 expression is constitutive through the mitotic cell cycle, which is consistent with a role for the protein in cell growth. CaSSD1 rescues the swi4ts defect in an ssd1-d background when expressed from its own promoter on a single-copy plasmid and under the same conditions can rescue mutations in genes encoding protein phosphatase type 2A catalytic subunits. These data suggest that CaSSD1, like its S. cerevisiae homologue, can limit the effect of mutations on a variety of cellular processes.