THE 9-KDA PHOSPHOPROTEIN OF PHOTOSYSTEM-II - GENERATION AND CHARACTERIZATION OF CHLAMYDOMONAS MUTANTS LACKING PSII-H AND A SITE-DIRECTED MUTANT LACKING THE PHOSPHORYLATION SITE

The chloroplast gene psbH encodes a 9-10 kDa thylakoid membrane protei n (PSII-H) that is associated with photosystem II and is subject to li ght-dependent phosphorylation at a threonine residue located on the st romal side of the membrane. The function of PSII-H is not known, neith er is it clear what regulatory role phosphorylation may play in the co ntrol of PSII activity. Using particle gun-mediated transformation, we have created chloroplast transformants of Chlamydomonas reinhardtii i n which the synthesis of PSII-H is prevented by the disruption of psbH , or in which the phosphorylatable threonine is replaced by alanine th rough site-directed mutagenesis of the gene. The mutants lacking PSII- H have a photosystem II-deficient phenotype, with no detectable functi oning PSII complex present in whole cells or isolated thylakoid membra nes. In contrast, the alanine mutant (T3A) grows photoautotrophically, and PSII activity is comparable to wild-type cells as determined by v arious biochemical and biophysical assays. (C) 1998 Elsevier Science B .V.