Gene sequence for the 9 kDa component of Photosystem II from the cyanobacterium Phormidium laminosum indicates similarities between cyanobacterial and other leader sequences |
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Authors: | T. P. Wallace A. C. Stewart D. Pappin C. J. Howe |
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Affiliation: | (1) Department of Biochemistry, University of Cambridge, Tennis Court Road, CB2 1QW Cambridge, UK;(2) Department of Biochemistry, University of Leeds, LS2 9JT Leeds, UK;(3) Present address: Elsevier Publications, 68 Hills Road, CB2 1LA Cambridge, UK |
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Abstract: | Summary A 9 kDa polypeptide which is loosely attached to the inner surface of the thylakoid membrane and is important for the oxygen-evolving activity of Photosystem II in the thermophilic cyanobacterium Phormidium laminosum has been purified, a partial amino acid sequence obtained and its gene cloned and sequenced. The derived amino acid sequence indicates that the 9 kDa polypeptide is initially synthesised with an N-terminal leader sequence of 44 amino acids to direct it across the thylakoid membrane. The leader sequence consists of a positively charged N-terminal region, a long hydrophobic region and a typical cleavage site. These features have analogous counterparts in the thylakoid-transfer domain of lumenal polypeptides from chloroplasts of higher plants. These findings support the view of the proposed function of this domain in the two-stage processing model for import of lumenal, nuclear-encoded polypeptides. In addition, there is striking primary sequence homology between the leader sequences of the 9 kDa polypeptide and those of alkaline phosphatase (from the periplasmic space of Escherichia coli) and, particularly in the region of the cleavage site, the 16 kDa polypeptide of the oxygen-evolving apparatus in the thylakoid lumen of spinach chloroplasts. |
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Keywords: | Cyanobacteria Evolution Thylakoid Leader sequence Photosystem II |
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