The non-reductive uptake of several siderophores (ferrioxamine B. ferrichro
me, triacetylfusarinine C and ferricrocin) by various strains of Saccharomy
ces cerevisiae was studied, Several aspects of siderophore transport were e
xamined, including specificity of transport, regulation of transport and in
tracellular localization of the ferri-siderophores, Ferrioxamine B was take
n up preferentially via the products of the SIT1 gene and triacetylfusarini
ne C by the TAF1 gene product, but the specificity was not absolute, Ferric
hrome and ferricrocin uptake was not dependent on a single major facilitato
r superfamily (MFS) gene product, The apparent specificity of transport was
strongly dependent on the genetic background of the cells, Non-reductive u
ptake of siderophores was induced under more stringent conditions (of iron
deprivation) than was the reductive uptake of ferric citrate. Regulation of
transport depended on the transcriptional factors Aft1 and Tup1/Ssn6, Cell
s disrupted for the TUP? or SSN6 genes were constitutively derepressed for
the uptake of ferrichrome, ferricrocin or ferrioxamine B, but not for the u
ptake of triacetylfusarinine C, Cells bearing the AFT1(up) mutation accumul
ated large amounts of ferric siderophores, Intracellular decomplexation of
the siderophores occurred when transcription of the AFT1(up) gene was repre
ssed. Ferrioxamine B and ferrichrome seemed to accumulate in an endosomal c
ompartment, as shown by biochemical studies and by confocal microscopy stud
y of cells loaded with a fluorescent derivative of ferrichrome, Endocytosis
was, however, not involved in the non-reductive uptake of siderophores.