Effect of precursor protein phosphorylation on import into isolated chloroplasts from Chlamydomonas

In higher plants, chloroplast-destined precursor proteins are thought to be phosphorylated. Mediated by a specific 14-3-3 protein, these phosphorylate d proteins hind to the chloroplast surface and are subsequently imported in to the chloroplast. We demonstrate that also in the green alga Chlamydomona s reinhardtii the precursor of the small subunit of ribulose-1,5-bisphospha te carboxylase becomes phosphorylated by a plant protein kinase and that th e phosphorylation site is located in the transit peptide. The phosphorylati on status of the precursor protein regulates its import into chloroplasts e specially at an early step during this process. The possible physiological function is discussed. (C) 2001 Federation of European Biochemical Societie s. Published by Elsevier Science B.V. All rights reserved.