FUNCTIONAL EXPRESSION CLONING AND CHARACTERIZATION OF SFT, A STIMULATOR OF FE TRANSPORT

A stimulator of Fe transport (SFT) was identified by functional expres sion cloning in Xenopus oocytes, SFT-mediated transport has properties defined for transferrin-independent Fe uptake, but its cytolocalizati on in recycling endosomes and the observed stimulation of transferrin- bound Fe assimilation indicate a key role in intracellular Fe membrane transport as well. SFT has six predicted transmembranous domains and a functionally important RExxE motif that resembles domains involved i n yeast Fe transport and Fe-binding by ferritin L-chains. The observat ion that SFT oligomerizes, along with other structural and mechanistic features, suggests it may be a member of either the ATP-binding casse tte or cation diffusion facilitator families. The 3' untranslated regi on of SFT contains a translation inhibitory element and inhibition of SFT expression in Xenopus oocytes was found to be relieved by coinject ion of transcripts from other defined cDNAs that are also described in this report. SFT is the first component of the mammalian Fe membrane transport machinery to be identified.