Characterization of a cDNA Clone for the PsaE Gene from Barley and Plasma Desorption Mass Spectrometry of the Corresponding Photosystem I Polypeptide PSI-E
Photosystem I (PS I) preparations from barley contain polypeptides with apparent molecular masses of 82 (PSI-A and PSI-B), 18 (PSI-D), 16 (PSI-E), 14, 9.5 (PSI-H), 9 (PSI-C), 4, and 1.5 kDa (PSI-I) as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis (1, 2). The nomenclature used for the subunits is described in more detail by Møller et al. (3). In this paper we report the characterization of a cDNA clone for the PsaE gene encoding the 16-kDa polypeptide PSI-E. The molecular mass of the mature polypeptide is 10,821 Da when deduced from the nucleotide sequence. To test whether the discrepancy between the molecular mass determinations could be due to post-translational modification of the polypeptide, the isolated polypeptide was analyzed by plasma desorption mass spectrometry. It has previously been established that the N- and C-terminal amino acid residues of the PSI-E polypeptide are not modified (4)
KeywordsPsaE Gene Mature Polypeptide Plasma Desorption Mass Spectrometry Plasma Desorption Mass Spectrum
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