title: Molecular characterization of transketolase (EC 2.2.1.1) active in the Calvin cycle of spinach chloroplasts.
abstract: A cDNA encoding the Calvin cycle enzyme transketolase (TKL; EC 2.2.1.1) was isolated from Sorghum bicolor via subtractive differential hybridization, and used to isolate several full-length cDNA clones for this enzyme from spinach. Functional identity of the encoded mature subunit was shown by an 8.6-fold increase of TKL activity upon induction of Escherichia coli cells that overexpress the spinach TKL subunit under the control of the bacteriophage T7 promoter. Chloroplast localization of the cloned enzyme is shown by processing of the in vitro synthesized precursor upon uptake by isolated chloroplasts. Southern blot-analysis suggests that TKL is encoded by a single gene in the spinach genome. TKL proteins of both higher-plant chloroplasts and the cytosol of non-photosynthetic eukaryotes are found to be unexpectedly similar to eubacterial homologues, suggesting a possible eubacterial origin of these nuclear genes. Chloroplast TKL is the last of the demonstrably chloroplast-localized Calvin cycle enzymes to have been cloned and thus completes the isolation of gene probes for all enzymes of the pathway in higher plants.
authors.affiliation: Institut für Pflanzenphysiologie, Berlin, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Flechner
authors.forename: U
authors.initials: U
authors.lastname: Dressen
authors.forename: P
authors.initials: P
authors.lastname: Westhoff
authors.forename: K
authors.initials: K
authors.lastname: Henze
authors.forename: C
authors.initials: C
authors.lastname: Schnarrenberger
authors.forename: W
authors.initials: W
authors.lastname: Martin
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D002736:Chloroplasts / Q000201:enzymology* / Q000235:genetics; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000235:genetics; D017343:Genes, Plant / Q000235:genetics; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010788:Photosynthesis / Q000235:genetics; D010802:Phylogeny; D011498:Protein Precursors / Q000378:metabolism; D011993:Recombinant Fusion Proteins; D017422:Sequence Analysis, DNA; D018724:Spinacia oleracea / Q000201:enzymology / Q000235:genetics*; D014174:Transketolase / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism
chemical_list: D011498:Protein Precursors; D011993:Recombinant Fusion Proteins; D014174:Transketolase