title: The DNA-compacting protein DCP68 from soybean chloroplasts is ferredoxin:sulfite reductase and co-localizes with the organellar nucleoid.
abstract: The multiple copies of the chloroplast genome (plastome) are condensed and organized into nucleoids by a set of proteins. One of these, the DNA-binding protein DCP68 from soybean, has previously been shown to compact DNA and to inhibit DNA synthesis in vitro. N-terminal amino acid analysis and the absorption spectrum of the purified protein suggest that DCP68 is the siroheme protein sulfite reductase, a ferredoxin-dependent enzyme that participates in sulfur assimilation for cysteine and methionine biosynthesis. The in vivo association of this protein with chloroplast nucleoids was confirmed by immuno-colocalization with antibodies against sulfite reductase from Arabidopsis thaliana. These results suggest that DCP68 is a bifunctional chloroplast protein that participates in reductive sulfur assimilation and plays a role in organellar nucleoid organization. The fact that dephosphorylation by alkaline phosphatase affects the binding of purified DCP68 to DNA in vitro might be indicative of the way the interaction of the protein with the nucleoid is regulated in vivo.
authors.affiliation: Department of Chemistry and Biochemistry, University of Southern Mississippi, Hattiesburg 39406-5043, USA.
authors.forename: Cecilia L
authors.initials: CL
authors.lastname: Chi-Ham
authors.forename: Mignon A
authors.initials: MA
authors.lastname: Keaton
authors.forename: Gordon C
authors.initials: GC
authors.lastname: Cannon
authors.forename: Sabine
authors.initials: S
authors.lastname: Heinhorst
mesh_terms: D000595:Amino Acid Sequence; D029681:Arabidopsis Proteins; D002736:Chloroplasts / Q000201:enzymology / Q000235:genetics*; D018742:DNA, Chloroplast / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D050862:Oxidoreductases Acting on Sulfur Group Donors / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D016415:Sequence Alignment; D020539:Sequence Analysis, Protein; D017386:Sequence Homology, Amino Acid; D030262:Soybean Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D013025:Glycine max / Q000201:enzymology / Q000235:genetics*; D013057:Spectrum Analysis; D050889:Sulfite Reductase (Ferredoxin)
chemical_list: D029681:Arabidopsis Proteins; D018742:DNA, Chloroplast; D004268:DNA-Binding Proteins; D030262:Soybean Proteins; D050862:Oxidoreductases Acting on Sulfur Group Donors; C488954:SIR protein, Arabidopsis; D050889:Sulfite Reductase (Ferredoxin)