title: An Arabidopsis thaliana cDNA encoding PS II-X, a 4.1 kDa component of photosystem II: a bipartite presequence mediates SecA/delta pH-independent targeting into thylakoids.
abstract: Higher plant photosystem II preparations contain a 4.1 kDa polypeptide (subunit X) associated with the oxygen-evolving core complex. We describe the isolation of a cDNA encoding PS II-X from Arabidopsis thaliana, in which the C-terminal region is highly homologous to partially sequenced PS II-X from wheat and spinach. The mature protein of 42 residues is preceded by a 74-residue, bipartite presequence similar to those involved in the targeting of nuclear-encoded thylakoid lumen proteins, although hydrophobicity analysis indicates the presence of a single transmembrane span in the mature protein. Moreover, import of pre-PS II-X into the thylakoid membrane of isolated chloroplasts is unaffected by inhibitors of either the Sec- or delta pH-dependent thylakoidal protein translocases, suggesting a spontaneous insertion mechanism. PS II-X appears to be encoded as a mature protein by the plastid genome in the chlorophyll a+c- containing alga, Odontella sinensis. We thus propose that the thylakoid transfer signal of Arabidopsis pre-PS II-X represents a recent acquisition, in phylogenetic terms, compared with signals of Sec-dependent lumenal proteins.
authors.affiliation: Department of Biological Sciences, University of Warwick, Goventry, UK.
authors.forename: S J
authors.initials: SJ
authors.lastname: Kim
authors.forename: D
authors.initials: D
authors.lastname: Robinson
authors.forename: C
authors.initials: C
authors.lastname: Robinson
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism*; D001386:Azides / Q000494:pharmacology; D001483:Base Sequence; D001693:Biological Transport, Active / Q000187:drug effects; D060365:Chloroplast Proteins; D002736:Chloroplasts / Q000378:metabolism; D018076:DNA, Complementary / Q000235:genetics* / Q000302:isolation & purification; D018744:DNA, Plant / Q000235:genetics* / Q000302:isolation & purification; D006863:Hydrogen-Ion Concentration; D007476:Ionophores / Q000494:pharmacology; D045342:Light-Harvesting Protein Complexes; D008565:Membrane Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D009550:Nigericin / Q000494:pharmacology; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D017386:Sequence Homology, Amino Acid
chemical_list: D001386:Azides; D060365:Chloroplast Proteins; D018076:DNA, Complementary; D018744:DNA, Plant; D007476:Ionophores; D045342:Light-Harvesting Protein Complexes; D008565:Membrane Proteins; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; C113691:photosystem II, PSII-X subunit; D009550:Nigericin