Abstract
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.
Highlights
Aliki Kapazoglou:J:, Francis Sagliocco§, and Leon Dure 11111 From the Department of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia 30602
It was shown that the cotton photosystem II (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, defining a new nuclear encoded lumenal protein and the smallest polypeptide of PSII reported to date
We report here the isolation and characterization of a nuclear gene from cotton encoding a putative 11-kDa protein, highly homologous in its C-terminal region to the 5-kDa PSII-T proteins from spinach and wheat and containing potential stroma and thylakoid targeting domains
Summary
Improvements in the resolution of polypeptides by SDS-PAGE techniques in the past few years has enabled the isolation of a number of low molecular weight proteins from PSII, mostly of unknown function and ranging in size from 3.6-10 kDa [2,3,4,5]. Many of these low mass PSII polypeptides are encoded in the nuclear genome in plants and algae, as judged by their absence in the four sequenced chloroplast genomes [1]. Tel.: 706-542-2086; Fax: 706-542-2090. 1 The abbreviations used are: PSII, photosystem II; PAGE, polyacrylamide gel electrophoresis; IB, import buffer
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
