Open AccessSaccharomyces cerevisiae Expresses Three Functionally Distinct Homologues of the Nramp Family of Metal Transporters
Author(s) -
Matthew E. Portnoy,
Xiu Fen Liu,
Valeria C. Culotta
Publication year - 2000
Publication title -
molecular and cellular biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.14
H-Index - 327
eISSN - 1067-8824
pISSN - 0270-7306
DOI - 10.1128/mcb.20.21.7893-7902.2000
Subject(s) - vacuole , saccharomyces cerevisiae , biology , yeast , transport protein , biochemistry , microbiology and biotechnology , transporter , intracellular , transmembrane protein , gene , cytoplasm , receptor
The baker's yeastSaccharomyces cerevisiae expresses three homologues of the Nramp family of metal transporters: Smf1p, Smf2p, and Smf3p, encoded bySMF1 ,SMF2 , andSMF3 , respectively. Here we report a comparative analysis of the yeast Smf proteins at the levels of localization, regulation, and function of the corresponding metal transporters. Smf1p and Smf2p function in cellular accumulation of manganese, and the two proteins are coregulated by manganese ions and theBSD2 gene product. Under manganese-replete conditions, Bsd2p facilitates trafficking of Smf1p and Smf2p to the vacuole, where these transport proteins are degraded. However, Smf1p and Smf2p localize to distinct cellular compartments under metal starvation: Smf1p accumulates at the cell surface, while Smf2p is restricted to intracellular vesicles. The third Nramp homologue, Smf3p, is quite distinctive. Smf3p is not regulated by Bsd2p or by manganese ions and is not degraded in the vacuole. Instead, Smf3p is down-regulated by iron through a mechanism that does not involve transcription or protein stability. Smf3p localizes to the vacuolar membrane independently of metal treatment, and yeast cells lacking Smf3p show symptoms of iron starvation. We propose that Smf3p helps to mobilize vacuolar stores of iron.