RESUMEN
The SSD1 gene of Saccharomyces (S.) cerevisiae is a polymorphic gene involved in many aspects of the yeast cell growth (Sutton et al., 1991). We found that ssd1 null mutant shows increased sensitivities of growth to trifluoperazine (TFP) and high concentration of Ca2+. A high-copy suppressor gene, HST1, for the TFP and Ca2+ sensitivities of ssd1 null mutant was cloned and sequenced. The HST1 gene encodes a polypeptide of 915 amino acids, and is identical to the NRC1/BRF1 gene in databases. The HST1 disrupted cells were viable, but they grew slowly in the presence of high levels of Ca2+, with notable morphological change. In addition, disruption of the gene in a ssd1 null mutant further increased the sensitivities of the cells to TFP and Ca2+. The results indicated the possibility that the SSD1 gene is involved in the tolerance mechanism to high concentration of Ca2+, and the HST1 gene participates with SSD1 by its functional redundancy in Ca2+ tolerance.