The Essential Cytosolic Iron-Sulfur Protein Nbp35 Acts without Cfd1 Partner in the Green Lineage*□S

In photosynthetic eukaryotes assembly components of iron-sulfur (Fe-S) cofactors have been studied in plastids and mito-chondria, but how cytosolic and nuclear Fe-S cluster proteins are assembled is not known. We have characterized a plant P loop NTPase with sequence similarity to Nbp35 of yeast and mammals, a protein of the cytosolicCfd1-Nbp35 complexmedi-ating Fe-S cluster assembly. Genome analysis revealed that NBP35 is conserved in the green lineage but thatCFD1 is absent. Moreover, plant and algal NBP35 proteins lack the characteris-tic CXXC motif in the C terminus, thought to be required for Fe-S cluster binding. Nevertheless, chemical reconstitution and spectroscopy showed that Arabidopsis (At) NBP35 bound a [4Fe-4S] cluster in the C terminus as well as a stable [4Fe-4S] cluster in theN terminus.Holo-AtNBP35was able to transfer an Fe-S cluster to an apoprotein in vitro. When expressed in yeast