The chloroplastic GrpE homolog of Chlamydomonas: two isoforms generated by differential splicing.
In eubacteria and mitochondria, Hsp70 chaperone activity is controlled by the nucleotide exchange factor GrpE. We have identified the chloroplastic GrpE homolog of Chlamydomonas, CGE1, as an approximately 26-kD protein coimmunoprecipitating with the stromal HSP70B protein. When expressed in Escherichia coli, CGE1 can functionally replace GrpE and interacts physically with DnaK. CGE1 is encoded by a single-copy gene that is induced strongly by heat shock and slightly by light. Alternative splicing generates two isoforms that differ only by two residues in the N-terminal part. The larger form is synthesized preferentially during heat shock, whereas the smaller one dominates at lower temperatures. Fractions of both HSP70B and CGE1 associate with chloroplast membranes in an ATP-sensitive manner. By colorless native PAGE and pulse labeling, CGE1 monomers were found to assemble rapidly into dimers and tetramers. In addition, CGE1 was found to form ATP-sensitive complexes with HSP70B of approximately 230 and approximately 120 kD, the latter increasing dramatically after heat shock.
Schroda
M
M
Institut de Biologie Physico-Chimique, Unité Propre de Recherche 1261, 13 rue Pierre et Marie Curie, 75005 Paris, France. ms@bop5.biologie.uni-freiburg.de
Vallon
O
O
Whitelegge
J P
JP
Beck
C F
CF
Wollman
F A
FA
D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D016825:Chlamydomonas reinhardtii / Q000235:genetics* / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics; D029968:Escherichia coli Proteins; D005816:Genetic Complementation Test; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000235:genetics* / Q000378:metabolism; D008027:Light; D008969:Molecular Sequence Data; D009154:Mutation; D010940:Plant Proteins; D020033:Protein Isoforms; D015800:Protozoan Proteins; D017386:Sequence Homology, Amino Acid
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C068113:GrpE protein, Bacteria; C489400:GrpE protein, E coli; D018840:HSP70 Heat-Shock Proteins; C102156:HSP70B protein, Chlamydomonas; D006360:Heat-Shock Proteins; D010940:Plant Proteins; D020033:Protein Isoforms; D015800:Protozoan Proteins; C063842:dnaK protein, E coli