CELL BIOLOGY: Popeye's Ribosomes Science; 2/4/2005; Hurtley, Stella M. Science 02-04-2005 Ribosomes are the central component of the protein synthesis machinery, and the efficient manufacture of ribosomes is crucial. These machines contain roughly 60 protein and RNA parts. The assembly of these parts occurs in the nucleus and involves importing proteins from the cytosol and placing them onto ribosomal RNA (rRNA); subsequently, the assembled small and large ribosomal subunits are exported to the cytosol. Two groups describe an unanticipated link in this chain of events--iron-sulfur (Fe-S) cluster biosynthesis. In a screen for ribosomal export mutants, Yarunin et al. found that genes implicated in Fe-S cluster biosynthesis in the cytosol are needed for ribosomal export. In particular, the protein Rli1 requires a Fe-S cluster to promote rRNA processing and small ribosomal subunit export. Kispal et al. also implicate Rli1 in the export of ribosomal subunits from the nucleus. In addition, they present evidence that this explains why Fe-S cluster biogenesis is an essential function and thus why mitochondria (where Fe-S cluster biogenesis originates) are essential. -- SMH EMBO J. 10.1038/sj.emboj.7600540; 10.1038/sj.emboj.7600541 (2005). Copyright © 2005 by the American Association for the Advancement of Science