Targeting of a human iron-sulfur cluster assembly enzyme, nifs, to different subcellular compartments is regulated through alternative AUG utilization

Iron-sulfur clusters are prosthetic groups that are required for the functi on of numerous enzymes in the cell, including enzymes important in respirat ion, photosynthesis, and nitrogen fixation. Here we report cloning of the h uman homolog of NifS, a cysteine desulfurase that is proposed to supply the inorganic sulfur in iron-sulfur clusters, In human cells, different forms of NifS that localize either to mitochondria or to the cytosol and nucleus ave synthesized from a single transcript: through initiation et;alternative in-frame AUGs, and initiation site selection varies according to the pn of the medium or cytosol. Thus, a novel form of translational regulation perm its rapid redistribution of NifS proteins into different compartments of th e cell in response to changes in metabolic status.