CHARACTERIZATION OF AN ARABIDOPSIS CDNA-ENCODING A THYLAKOID LUMEN PROTEIN RELATED TO A NOVEL PENTAPEPTIDE REPEAT FAMILY OF PROTEINS

We have cloned an Arabidopsis cDNA encoding a novel thylakoid lumen pr otein, P17.4, that has been previously isolated from lumen extracts of spinach chloroplasts. The protein is synthesised with a bipartite pre sequence containing a Sec-type Lumen-targeting signal peptide and the precursor protein is imported into the Lumen of pea chloroplasts. The encoded protein is homologous to an Anabaena protein that is essential for correct glycolipid localisation, and is also related to at least 16 unassigned open reading frames in Synechocystis. This family of pro teins is characterised by the presence of numerous pentapeptide repeat s with the consensus structure AXLXX, and its members are predicted to be located in the cytosol, plasma membrane and periplasm/lumen. P17.4 is therefore the first higher plant member of an extended family of p utative cyanobacterial proteins that may serve important roles in lipi d transport or assembly. (C) 1998 Federation of European Biochemical S ocieties.