Mitochondrial Isa2p plays a crucial role in the maturation of cellular iron-sulfur proteins.

The assembly of iron-sulfur (Fe/S) clusters in a living cell is mediated by a complex machinery which, in eukaryotes, is localised within mitochondria. Here, we report on a new component of this machinery, the protein Isa2p of the yeast Saccharomyces cerevisiae. The protein shares sequence similarity with yeast Isa1p and the bacterial IscA proteins which recently have been shown to perform a function in Fe/S cluster biosynthesis. Like the Isa1p homologue, Isa2p is localised in the mitochondrial matrix as a soluble protein. Deletion of the ISA2 gene results in the loss of mitochondrial DNA and a strong growth defect. Simultaneous deletion of the ISA1 gene does not further exacerbate this growth phenotype suggesting that the Isa proteins perform a non-essential function. When Isa2p was depleted by regulated gene expression, mtDNA was maintained, but cells grew slowly on non-fermentable carbon sources. The maturation of both mitochondrial and cytosolic Fe/S proteins was strongly impaired in the absence of Isa2p. Thus, Isa2p is a new member of the Fe/S cluster biosynthesis machinery of the mitochondrial matrix and may be involved in the binding of an intermediate of Fe/S cluster assembly.