Import and processing of the precursor of the Rieske FeS protein of tobacco chloroplasts

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Abstract
CDNA clones encoding the precursor of the Rieske FeS protein of tobacco chloroplasts have been characterised and shown to derive from two different genes. The 5′ ends of the corresponding transcripts have been cloned using primer extension and PCR. The nucleotide sequences of the cDNAs (and their 5′ extensions) predict precursors for the tobacco proteins which differ in 4 amino acid residues out of a total of 228 residues and show high homology with the pea and spinach precursors. The tobacco precursor proteins contain N-terminal presequences of 49 amino acid residues which lack 17 amino acid residues present at the N-terminus of the spinach presequence. The 26 kDa precursor obtained by transcription and translation of one of these cDNAs in vitro was efficiently imported and correctly processed to the mature 20 kDa protein by isolated pea or tobacco chloroplasts. The precursor was also processed to its mature size by a peptidase present in the stroma of chloroplasts.