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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 cerevisiae. 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.

Section: Discussionmentioning

confidence: 99%

Alkaline Response Genes of Saccharomyces cerevisiaeand Their Relationship to the RIM101 Pathway

Lamb¹,

Xu²,

Diamond³

et al. 2001

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“…5A). Arn4 is a paralog of Arn1 and facilitates the uptake of the bacterial siderophore enterobactin in yeast (46,47). Unlike Arn1 and Arn3, Arn4 is expressed exclusively on the plasma membrane, whether enterobactin is present in the growth medium or not (Fig.…”

Section: Requirement Of Residues In the Arn1mentioning

confidence: 99%

Gga2 Mediates Sequential Ubiquitin-independent and Ubiquitin-dependent Steps in the Trafficking of ARN1 from the trans-Golgi Network to the Vacuole

Deng¹,

Guo²,

Watson

et al. 2009

In Saccharomyces cerevisiae, ARN1 encodes a transporter for the uptake of ferrichrome, an important nutritional source of iron. In the absence of ferrichrome, Arn1p is sorted directly from the trans-Golgi network (TGN) to the vacuolar lumen via the vacuolar protein-sorting pathway. Arn1p is mis-sorted to the plasma membrane in cells lacking Gga2p, a monomeric clathrin-adaptor protein involved in vesicular transport from the TGN. Although Ggas have been characterized as ubiquitin receptors, we show here that ubiquitin binding by Gga2 was not required for the TGN-to-endosome trafficking of Arn1, but it was required for subsequent sorting of Arn1 into the multivesicular body. In a ubiquitin-binding mutant of Gga2, Arn1p accumulated on the vacuolar membrane in a ubiquitinated form. The yeast epsins Ent3p and Ent4p were also involved in TGN-to-vacuole sorting of Arn1p. Amino-terminal sequences of Arn1p were required for vacuolar protein sorting, as mutation of ubiquitinatable lysine residues resulted in accumulation on the vacuolar membrane, and mutation of either a THN or YGL sequence resulted in mis-sorting to the plasma membrane. These studies suggest that Gga2 is involved in sorting at both the TGN and multivesicular body and that the first step can occur without ubiquitin binding.

“…Four siderophore transporters (Arn1p, Arn2p/Taf1p, Arn3p/ Sit1p, and Arn4p/Enb1p) have been reported in S. cerevisiae, collectively responsible for the uptake of a range of siderophores of different structures and chemical properties (16,(31)(32)(33)(34). These proteins belong to the major facilitator superfamily, whose members have been found in many organisms.…”

mentioning

confidence: 99%

Characterization and Functional Analysis of the Siderophore-Iron Transporter CaArn1p in Candida albicans

Bai

Zheng

et al. 2002

Siderophores are small organic compounds with high affinity for ferric iron. Microorganisms commonly acquire iron via siderophore secretion and uptake. Here we report the characterization of the siderophore transporter CaArn1p in the fungal pathogen Candida albicans. Deletion of CaARN1 reduced the ability of C. albicans to use iron bound to the hydroxamate-type siderophore ferrichrome and abolished it when two high-affinity iron permease genes (CaFTR1 and CaFTR2) were also deleted, indicating a role of CaArn1p as well as the permeases in ferrichrome-iron uptake. Caarn1⌬ (but not Caftr1⌬Caftr2⌬) assimilated iron from another hydroxamate-type siderophore, ferrioxamine B, suggesting that iron uptake from this compound depends on the permeases, but not on CaArn1p. Northern blot analysis revealed that the transcription repressor CaTup1p repressed CaARN1 expression under iron-replete conditions via the DNA-binding protein Rfg1p. Green fluorescent protein-tagged CaArn1p was observed predominantly in the plasma membrane, with some in the cytoplasm as distinct spots. The number of these spots increased with the increase in ferrichrome concentration, suggesting that CaArn1p internalization might be a mechanism for ferrichrome-iron uptake or for recycling the transporter. Caarn1⌬ did not show reduced virulence when injected into the blood stream of mice, implying that CaArn1p is not required for iron uptake along this route of infection.