THE 64 KDA POLYPEPTIDE OF SPINACH MAY NOT BE THE LHCII KINASE, BUT A LUMEN-LOCATED POLYPHENOL OXIDASE

Phosphorylation of chlorophyll alb-binding proteins of the of photosys tem II light-harvesting assembly controls the energy distribution betw een the two photosystems as well as the turnover of thylakoid membrane proteins, The LHCII kinase, suggested to be a 64 kDa protein, is ligh t-regulated by a mechanism involving reduction of plastoquinone and th e participation of the cytochrome b(6)/f complex, A cDNA encoding that protein has been isolated from a lambda gt11-based library made from spinach polyadenylated RNA using a two-step strategy involving screeni ng by polyclonal monospecific antisera and plaque hybridization, The p rotein of 73.1 kDa molecular mass represents a precursor which contain s a bipartite transit peptide of 101 amino acid residues (11.0 kDa) th at directs the protein into the thylakoid lumen, It can be phosphoryla ted in vitro, and exhibits significant homology to plant polyphenol ox idases, not to kinases, The gene was therefore designated PpoA, Reinve stigation of components in the molecular mass range of 50-70 kDa discl osed five additional proteins which can accompany kinase-active cytoch rome b(6)/f, photosystem II and AMS [1] preparations. Four Of them can be phosphorylated in vitro; two with apparent molecular masses of 53 and 66 kDa are capable of phosphorylation, and represent new, yet unid entified proteins.