The nuclear-encoded SDH2-RPS14 precursor is proteolytically processed between SDH2 and RPS14 to generate maize mitochondrial RPS14

In maize, the functional gene encoding mitochondrial ribosomal protein S14 (rps14) has been translocated to the nucleus where it became integrated bet ween both exons of a gene encoding the iron-sulfur subunit of succinate deh ydrogenase (sdh2). Two transcripts are generated from this locus by alterna tive splicing. One transcript encodes a precursor for a functional SDH2 pro tein, while the second transcript encodes a chimeric SDH2(t)-RPS14 precurso r protein. In this paper we show that the same mitochondrial targeting pres equence is able to direct the import of both precursors into isolated mitoc hondria and is removed during import. This processing event generates a 28 kDa protein fi om the SDH2 precursor, which corresponds to the iron-sulfur subunit of respiratory complex II present in maize mitochondria. In additio n to cleavage of the presequence, the chimeric precursor undergoes proteoly tical processing between SDH2 and RPS14. This processing generates RPS14, w hich is found assembled into mitochondrial ribosomes, and a truncated SDH2 protein which is degraded. Therefore, our results support a role of the SDH 2 domain in the chimeric precursor only in providing a mitochondrial target ing function for RPS14. (C) 2000 Academic Press.