Transit Peptides of Thylakoid Luminal Proteins: the Sites of Stromal Processing are Conserved among Higher Plants

The amino terminal of the transport intermediate of the 23-kDa protein of PSII, which was generated by stromal processing, was determined by radiosequencing in order to identify the site of processing of its precursor. The site was located in the central region of the transit peptide. The primary structure of the processing site included a motif that is common to the processing sites of transit peptides of various stromal proteins. This common motif was also found in the transit pep-tides of other thylakoid luminal proteins, an indication of its conservation among higher plants. A common secondary structure, /taurn//?-sheet/ct-helix, was predicted from the amino acid se-quence around the consensus motif. This structural similarity between stromal and thylakoid luminal proteins suggests that the sequences are under a common selective pressure to maintain these sites of cleavage by a stromal processing peptidase. Key words: Pea (Pisum sativum L. var. Alaska) — Processing site — Protein transport — Thyla-koid luminal proteins — Transit peptide — Two-step processing. Chloroplast proteins that are encoded by the nuclear genome are synthesized in the cytosol as larger precursor forms with transit peptides at their amino terminals, an