Alkaline response genes of Saccharomyces cerevisiae and their relationship to the RIM101 pathway

Environmental pH exerts broad control over growth and differentiation, but the molecular responses to external pH changes are poorly understood. Here we have used open reading frame macroarray hybridization to identify alkaline response genes in Saccharomyces cer evisiae. Northern or lacZ fusion assays confirmed the alkaline induction of two ion pump genes (ENA1 and VMA4), several ion limitation genes (CTR3, FRE1, PHO11/12, and PHO84), a siderophore-iron transporter gene (ARN4/ENB1), two transcription factor genes (NRG2 and TIS11), and two predicted membrane protein genes (YAR068W/YHR214W and YOL154W). Unlike ENA1 and SHC1, these new alkaline response genes are not induced by high salinity. The known pH-responsive genes in other fungi depend on the conserved PacC/Rim101p transcription factor, but induction of several of these new genes relied upon Rim101p-independent pH signaling mechanisms. Rim101p-dependent genes were also dependent on Rim13p, a protease required for Rim101p processing. The Rim101p-dependent gene VMA4 is required for growth in alkaline conditions, illustrating how Rim101p may control adaptation. Because Rim101p activates ion pump genes, we tested the role of RIM101 in ion homeostasis and found that RIM101 promotes resistance to elevated cation concentrations. Thus, gene expression surveys can reveal new functions for characterized transcription factors in addition to uncovering physiological responses to environmental conditions.