Photosystem I reaction‐centre proteins contain leucine zipper motifs

Abstract
The photosystem I (PS I) reaction‐centre polypeptides, encoded by the psaA and psaB genes, are shown to contain several highly conserved leucine repeats, consisting of a leucine residue every seventh amino acid, similar to the leucine zipper motifs known to mediate DNA‐binding polypeptide dimerisation. In each of the PSI reaction‐centre subunits the leucine zipper motif precedes highly conserved cysteine residues which have been proposed to ligate the interpolypeptide [4Fe‐4S] centre, Fx. We propose that PS I reaction‐centre dimerisation and [4Fe‐4S] centre formation are mediated through the leucine zipper.