Desferrioxamine-mediated Iron Uptake in Saccharomyces cerevisiae

Abstract

In the yeast Saccharomyces cerevisiae, uptake of iron is largely regulated by the transcription factor Aft1. cDNA microarrays were used to identify new iron and AFT1-regulated genes. Four homologous genes regulated as part of the AFT1-regulon (ARN1-4) were predicted to encode members of a subfamily of the major facilitator superfamily of transporters. These genes were predicted to encode proteins with 14 membrane spanning domains and were from 26 to 53% identical at the amino acid level. ARN3 is identical to SIT1, which is reported to encode a ferrioxamine B permease. Deletion of ARN3 did not prevent yeast from using ferrioxamine B as an iron source; however, deletion of ARN3 and FET3, a component of the high affinity ferrous iron transport system, did prevent uptake of ferrioxaminebound iron and growth on ferrioxamine as an iron source. The siderophore-mediated transport system and the high affinity ferrous iron transport system were localized to separate cellular compartments. Epitopetagged Arn3p was expressed in intracellular vesicles that co-sediment with the endosomal protein Pep12. In contrast, Fet3p was expressed on the plasma membrane and was digested by extracellular proteases. These data indicate that S. cerevisiae has two pathways for ferrrioxamine-mediated iron uptake, one occurring at the plasma membrane and the other occurring in an intracellular compartment.

Aft1p and Aft2p Mediate Iron-responsive Gene Expression in Yeast through Related Promoter Elements

“…These include individual genes that are activated by the AFT1-1 up allele, genes within the iron regulon that are activated indirectly in response to cobalt stress and genes that are activated in a strain that lacks a functional Yfh1p, a protein that is involved in mitochondrial iron-sulfur cluster formation (10,12,13,14,25,26). There are, however, differences between these data sets.…”

Siderophore uptake and use by the yeast Saccharomyces cerevisiae

“…The present study suggests that the siderophore FOB is associated with an endosomal compartment when it accumulates inside the cells. Another study (Yun et al, 2000a) showed that Sit1p is also associated with the late endosome compartment. We used AFT1 up mutant cells, which accumulate large amounts of siderophores.…”

“…This would explain why iron was released from FOB within the cells when the AFT1 up gene on a plasmid was turned off in a ∆aft1 strain loaded with FOB. Yun et al (2000a) proposed that Sit1p is involved downstream of the uptake system for FOB, which itself could involve endocytosis. However, this possibility can be ruled out since a mutant completely blocked for endocytosis showed no defect in siderophore uptake.…”

“…8). Yun et al (2000a) recently showed that Sit1p was mostly associated with an internal compartment (probably late endosome), unlike the Fet3p-Ftr1p complex (components of the reductive uptake system), which was mostly associated with the plasma membrane fraction. Therefore, we tested the possibility that the uptake of siderophore depended on endocytosis.…”

The CaCTR1 gene is required for high-affinity iron uptake and is transcriptionally controlled by a copper-sensing transactivator encoded by CaMAC1

“…This iron uptake system is not dependent upon copper and consists of four transporter proteins, ScArn1-4p (Heymann et al, 1999;Lesuisse et al, 1998;Yun et al, 2000b). Each transporter displays varying specificity to a range of ferri-siderophores from both the hydroxamate and catechol classes (Yun et al, 2000a). However, siderophore production has never been unequivocally proven in S. cerevisiae, so the organism may rely on those that are produced by other species.…”