Suppressor analysis of the mpt5/htr1/uth4/puf5 deletion in Saccharomyces cerevisiae

The MPT5/HTR1/UTH4/PUF5 gene encodes an RNA-binding Puf-family protein in Saccharomyces cerevisiae. The Δmpt5 cells exhibit pleiotropic phenotypes, including the G2/M arrest of the cell cycle and weakened cell wall at high temperatures. The Δmpt5 disruptant was also hydroxyurea (HU) sensitive. In this study we screened deletion suppressors to rescue the temperature sensitivity of Δmpt5, and identified dsf1 (YEL070W), dsf2 (YBR007C), sir2, sir3, sir4 and swe1. Multicopy suppressors identified were PKC1 and its upstream genes, but not the downstream MAPK cascade genes. The overexpression of PKC1, however, did not suppress the HU sensitivity of Δmpt5. In contrast, both the HU- and temperature-sensitivities of a-type Δmpt5 cells were suppressed by each sir deletion or a multicopy of MATα2, suggesting that a diploid-type expression is involved. We found that a diploid-specific IME4 gene encoding an RNA-modifying protein was responsible for the suppression of the temperature sensitivity, but not of the HU sensitivity. Furthermore, the suppression of the HU sensitivity depended on PUF4, another Puf-family gene, and overexpression of PUF4 suppressed only the HU sensitivity of Δmpt5. The protein level of Puf4 was not affected by the sir mutation. Thus, these Ime4 and Puf4 proteins play complementary roles to rescue the defects in Δmpt5 Δsir cells.