Masson J Y, Ramotar D
Maisonneuve-Rosemont Hospital Research Center, Université de Montreal, Montreal, Quebec H1T 2M4, Canada.
Genetics. 1998 Jun;149(2):893-901. doi: 10.1093/genetics/149.2.893.
Yeast cells deficient in the transcriptional activator Imp2p are viable, but display marked hypersensitivity to a variety of oxidative agents. We now report that imp2 null mutants are also extremely sensitive to elevated levels of the monovalent ions, Na+ and Li+, as well as to the divalent ions Ca2+, Mn2+, Zn2+, and Cu2+, but not to Cd2+, Mg2+, Co2+, Ni2+, and Fe2+, as compared to the parent strain. We next searched for multicopy suppressor genes that would allow the imp2Delta mutant to grow under high salt conditions. Two genes that independently restored normal salt-resistance to the imp2Delta mutant, ENA1 and HAL3, were isolated. ENA1 encodes a P-type ion pump involved in monovalent ion efflux from the cell, while HAL3 encodes a protein required for activating the expression of Ena1p. Neither ENA1 nor HAL3 gene expression was positively regulated by Imp2p. Moreover, the imp2 ena1 double mutant was exquisitely sensitive to Na+/Li+ cations, as compared to either single mutant, implying that Imp2p mediates Na+/Li+ cation homeostasis independently of Ena1p.
缺乏转录激活因子Imp2p的酵母细胞能够存活，但对多种氧化试剂表现出明显的超敏反应。我们现在报告，与亲本菌株相比，imp2基因缺失突变体对单价离子Na⁺和Li⁺以及二价离子Ca²⁺、Mn²⁺、Zn²⁺和Cu²⁺的浓度升高也极为敏感，但对Cd²⁺、Mg²⁺、Co²⁺、Ni²⁺和Fe²⁺不敏感。接下来，我们寻找能使imp2Δ突变体在高盐条件下生长的多拷贝抑制基因。分离出了两个能独立恢复imp2Δ突变体正常耐盐性的基因，即ENA1和HAL3。ENA1编码一种参与细胞单价离子外流的P型离子泵，而HAL3编码激活Ena1p表达所需的一种蛋白质。Imp2p对ENA1和HAL3基因的表达均无正向调控作用。此外，与任一单突变体相比，imp2 ena1双突变体对Na⁺/Li⁺阳离子极为敏感，这意味着Imp2p独立于Ena1p介导Na⁺/Li⁺阳离子稳态。
