Isa1p is a component of the mitochondrial machinery for maturation of cellular iron-sulfur proteins and requires conserved cysteine residues for function

In eukaryotes, mitochondria execute a central task in the assembly of cellu lar iron-sulfur (Fe/S) proteins. The organelles synthesize their own set of Fe/S proteins, and they initiate the generation of extramitochondrial Fe/S proteins, In the present study, we identify the mitochondrial matrix prote in Isa1p of Saccharomyces cerevisiae as a new member of the Fe/S cluster bi osynthesis machinery, Isa1p belongs to a family of homologous proteins pres ent in prokaryotes and eukaryotes. Deletion of the ISA1 gene results in the loss of mitochondrial DNA precluding the use of the Delta isa1 strain for functional analysis. Cells in which Isa1p was depleted by regulated gene ex pression maintained the mitochondrial DNA, yet the cells displayed retarded growth on nonfermentable carbon sources, This finding indicates the import ance of Isa1p for mitochondrial function. Deficiency of Isa1p caused a defe ct in mitochondrial Fe/S protein assembly. Moreover, Isa1p was required for maturation of cytosolic Fe/S proteins, Two cysteine residues in a conserve d sequence motif characterizing the Isa1p protein family were found to be e ssential for Isa1p function in the biogenesis of both intra- and extramitoc hondrial Fe/S proteins. Our findings suggest a function for Isa1p in the bi nding of iron or an intermediate of Fe/S cluster assembly.