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Structure and mutation of a gene encoding a Mr 33000 phycocyanin-associated linker polypeptide
Authors:Robert de Lorimier  Gerard Guglielmi  Donald A Bryant  S Edward Stevens Jr
Institution:(1) Department of Molecular and Cell Biology, The Pennsylvania State University, 16802 University Park, PA, USA;(2) Present address: Department of Molecular and Cellular Biology-Stanley/Donner ASU, University of California, 94720 Berkeley, CA, USA;(3) Present address: Institut Pasteur, 25-28 rue de Dr. Roux, F-75724 Paris Cedex 15, France;(4) Present address: Department of Biological Sciences, Memphis State University, 38152 Memphis, TN, USA
Abstract:The gene encoding a phycocyanin-associated linker polypeptide of Mr 33000 from the cyanobacterium Synechococcus sp. PCC 7002 was found to be located adjacent and 3prime to the genes encoding the agr and beta subunits of phycocyanin. The identity of this gene, designated cpcC, was proven by matching the amino-terminal sequence of the authentic polypeptide with that predicted by the nucleotide sequence. A cpcC mutant strain of this cyanobacterium was constructed. The effect of the mutation was to prevent assembly of half the total phycocyanin into phycobilisomes. By electron microscopy, phycobilisomes from this mutant were shown to contain rod substructures composed of a single disc of hexameric phycocyanin, as opposed to two discs in the wild type. It was concluded that the Mr 33000 linker polypeptide is required for attachment of the core-distal phycocyanin hexamer to the core-proximal one. Using absorption spectra of the wild type, CpcC, and phycocyanin-less phycobilisomes, the in situ absorbances expected for specific phycocyanin-linker complexes were calculated. These data confirm earlier findings on isolated complexes regarding the influence of linkers on the spectroscopic properties of phycocyanin.Abbreviations PC phycocyanin - PEC phycoerythrocyanin - AP allophycocyanin - SDS-PAGE polyacrylamide gel electrophoresis in the presence of sodium dodecylsulfate. Linker polypeptides are abbreviated according to Glazer (1985). L infX supY refers to a linker having a mass Y, located at a position X in the phycobilisome, where X can be R (rod), RC (rod or core), C (core) or CM (core to membrane). When necessary, the abbreviation for a linker is appended with that of its associated phycobiliprotein. Thus, L infR sup34.5PEC is a rod linker of Mr 34 500 that is associated with phycoerythrocyanin
Keywords:Cyanobacteria  Synechococcus sp  PCC 7002  Agmenellum quadruplicatum  Phycobilisome  Phycocyanin  Linker polypeptide  Photosynthetic antenna  Nucleotide sequence  Directed mutagenesis
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