PSII-T, a new nuclear encoded lumenal protein from photosystem II. Targeting and processing in isolated chloroplasts.
An intronless nuclear gene, psbT, isolated from cotton, encodes a putative 11-kDa protein (PSII-T) highly homologous in its C terminus to the N terminus of the partially sequenced PSII-T protein from spinach photosystem II. Analysis of the deduced amino acid sequence of cotton PSII-T revealed the presence of potential chloroplast stroma and thylakoid targeting domains and a putative mature PSII protein of 3.0 kDa, composed of only 28 amino acid residues. The cotton PSII-T 11-kDa precursor was synthesized in vitro in a wheat germ extract translation system, and the translation product was used in assays for protein imports into isolated pea chloroplasts. It was shown that the cotton PSII-T precursor was imported into the chloroplasts, processed to a mature form of approximately 3.0 kDa, agreeing with the predicted size from amino acid sequence analysis, and localized to the lumenal side of the thylakoid membrane, thus defining a new nuclear encoded lumenal protein and the smallest polypeptide of PSII reported to date. Processing of the PSII-T precursor occurred in two steps and involved the formation of a stromal intermediate of approximately 7.5 kDa, as predicted from primary structure analysis.
Kapazoglou
A
A
Department of Biochemistry and Molecular Biology, University of Georgia, Athens 30602, USA.
Sagliocco
F
F
Dure
L
L
D000595:Amino Acid Sequence; D001483:Base Sequence; D001692:Biological Transport; D002467:Cell Nucleus; D002736:Chloroplasts / Q000378:metabolism*; D017343:Genes, Plant; D003368:Gossypium / Q000235:genetics*; D008969:Molecular Sequence Data; D018532:Pisum sativum / Q000378:metabolism; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D045332:Photosystem II Protein Complex; D010940:Plant Proteins / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D018724:Spinacia oleracea / Q000235:genetics
D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; C093489:photosystem II, psbT subunit