Cloning and sequencing of spinach cDNA clones encoding the 20 kDa PS I polypeptide.

Apart from the 8 kDa subunit, which is of chloroplast origin, most of the small polypeptides of the PS I reaction center from higher plants are encoded in nuclear genes. We describe here the first nucleotide sequence of a nuclear component of this photosystem, the precursor of the 20 kDa protein. The deduced sequence of the large transit peptide (55-60 amino acids) is rich in serine/threonine residues and has a net positive charge, which are classical features of these precursors. The sequence itself is mainly hydrophilic, with no possibility of classical membrane-spanning alpha-helices; it exhibits an interesting stretch of five basic amino acids in close vicinity: Thr-Arg-Leu-Arg-Ser-Lys-Tyr-Lys-Ile-Lys-Tyr.