In organello and in vitro phosphorylation of chloroplast ribosomal proteins

Two chloroplast ribosomal proteins are phosphorylated in isolated chloroplast. One in the large subunit (L18) and one in the small subunit ( LS31 ). The phosphorylation is light dependent and occurs on a serine residue for both ribosomal proteins. These two proteins and other chloroplast ribosomal proteins are also phosphorylated in vitro using [gamma 32P]-ATP and a cAMP -dependent or a cAMP - independent protein kinase. The existence of a protein-kinase bound to chloroplast 70S ribosomes is also demonstrated, the enzyme is able to phosphorylate almost every chloroplast ribosomal protein.