Copper and iron are the limiting factors for growth of the yeast Saccharomyces cerevisiae in an alkaline environment.
Exposure of the yeast Saccharomyces cerevisiae to an alkaline environment represents a stress situation that negatively affects growth and results in an adaptive transcriptional response. We screened a collection of 4825 haploid deletion mutants for their ability to grow at mild alkaline pH, and we identified 118 genes, involved in numerous cellular functions, whose absence results in reduced growth. The list includes several key genes in copper and iron homeostasis, such as CCC2, RCS1, FET3, LYS7, and CTR1. In contrast, a screen of high-copy number plasmid libraries for clones able to increase tolerance to alkaline pH revealed only two genes: FET4 (encoding a low affinity transporter for copper, iron, and zinc) and CTR1 (encoding a high affinity copper transporter). The beneficial effect of overexpression of CTR1 requires a functional high affinity iron transport system, as it was abolished by deletion of FET3, a component of the high affinity transport system, or CCC2, which is required for assembly of the transport system. The growth-promoting effect of FET4 was not modified in these mutants. These results suggest that the observed tolerance to alkaline pH is because of improved iron uptake and indicate that both iron and copper are limiting factors for growth under alkaline pH conditions. Addition to the medium of micromolar concentrations of copper or iron ions drastically improved growth at high pH. Supplementation with iron improved somewhat the tolerance of a fet3 strain but was ineffective in a ctr1 mutant, suggesting the existence of additional copper-requiring functions important for tolerance to an alkaline environment.
Departament de Bioquímica i Biologia Molecular, Universitat Autònoma de Barcelona, Bellaterra, 08193 Barcelona, Spain.
Raquel
R
Serrano
Dolores
D
Bernal
Ernesto
E
Simón
Joaquín
J
Ariño
D001692:Biological Transport; D027682:Cation Transport Proteins / Q000378:metabolism; D002455:Cell Division; D003300:Copper / Q000378:metabolism*; D000079923:Copper Transporter 1; D004247:DNA / Q000737:chemistry; D004305:Dose-Response Relationship, Drug; D004926:Escherichia coli / Q000378:metabolism; D017353:Gene Deletion; D015723:Gene Library; D006238:Haploidy; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000378:metabolism*; D007700:Kinetics; D008954:Models, Biological; D009154:Mutation; D010957:Plasmids / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins
C490078:CTR1 protein, S cerevisiae; D027682:Cation Transport Proteins; D000079923:Copper Transporter 1; D011994:Recombinant Proteins; D029701:Saccharomyces cerevisiae Proteins; D003300:Copper; D004247:DNA; D007501:Iron