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

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.

Light-stimulated degradation of an unassembled Rieske FeS protein by a thylakoid-bound protease: the possible role of the FtsH protease.

“…Although it is still a matter of dispute whether the RlSP is an intrinsic or extrinsic membrane protein (Breyton et al, 1994;Madueiio et al, 1994;Cramer et al, 1996), it is widely accepted that the bulk of the protein, including the 2Fe-2S center that is active in redox reactions, faces the lumen. This topology is consistent with the RISP's role in shuttling electrons between the membrane-embedded heme group of Cyt b6 and the one exposed to the lumen of Cyt f. The RlSP is synthesized in the cytosol in a precursor form, with an N-terminal signal peptide that directs it to the chloroplast and mediates its post-translational translocation across the envelope (Maduetio et al, 1992). During or shortly after import, this signal peptide is proteolytically removed, and the mature protein undergoes further sorting and assembly processes, leading to its final association with other subunits of the cytochrome complex in the thylakoid membrane.…”

Inducible Repression of Nuclear-Encoded Subunits of the Cytochrome b6f Complex in Tobacco Reveals an Extraordinarily Long Lifetime of the Complex

“…As two highly homologous PetC isoforms exist in tobacco, which differ only in four amino acids and 15 nucleotides within the coding region, respectively (Madueño et al, 1992), we targeted both isoforms with our RNAi construct. The construct covered 211 nucleotides spanning positions 145 to 355 of the coding region of both isoforms.…”

The Rieske Fe/S Protein of the Cytochromeb /f Complex in Chloroplasts

“…The Rieske Fe/S protein of the cytochrome b 6 /f complex is an indispensable component of the photosynthetic electron transport chain in chloroplasts. It is a bitopic polypeptide that faces the stroma with only a few NH 2 -terminal residues and is anchored in the membrane with a single transmembrane helix (1).…”