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Published November 1, 1983 | Published
Journal Article Open

Primary structure of the M subunit of the reaction center from Rhodopseudomonas sphaeroides


The reaction center is a membrane-bound bacteriochlorophyll--protein complex that mediates the primary photochemical events in the photosynthetic bacterium Rhodopseudomonas sphaeroides. The previously determined amino-terminal sequences of the three subunits of the reaction center protein were used to design synthetic mixed oligonucleotide probes for the structural genes encoding the subunits. One of these probes was used to isolate and clone a fragment of DNA from R. sphaeroides that contained the gene encoding the M subunit. The nucleotide sequence of this gene was determined by the dideoxy method. In addition, a number of tryptic and chymotryptic peptides from the M protein were isolated and subjected to sequence analysis, and the sequence of the carboxyl terminus was determined. Together with the amino-terminal sequence, the data establish the primary structure of the M protein. The distribution of hydrophobic residues in the amino acid sequence suggests the presence of five membrane-spanning segments. A significant homology was found between the amino acid sequence of the M subunit and a thylakoid membrane protein (Mr 32,000) from spinach that has been implicated in herbicide and quinone binding.

Additional Information

© 1983 by the National Academy of Sciences. Contributed by G. Feher, July 25, 1983. We thank E. Abresch for the preparation of the RCs, E. Capuno-Tichy and L.-P. Li for assistance in peptide preparation and analysis, and R.F. Doolittle for the computer search for homologous protein sequences. This work was supported by grants from the National Institutes of Health (GM 13191 and 07313), the National Science Foundation (PCM 82-02811), the Office of Naval-Research (N00014-83-K-0079), and the U.S. Department of Agriculture (5901-0410-9-0378-0). The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

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