The core of chloroplast nucleoids contains architectural SWIB domain proteins.
A highly enriched fraction of the transcriptionally active chromosome from chloroplasts of spinach (Spinacia oleracea) was analyzed by two-dimensional gel electrophoresis and mass spectrometry to identify proteins involved in structuring of the nucleoid core. Among such plastid nucleoid-associated candidate proteins a 12-kD SWIB (SWI/SNF complex B) domain-containing protein was identified. It belongs to a subgroup of low molecular mass SWIB domain proteins, which in Arabidopsis thaliana has six members (SWIB-1 to SWIB-6) with predictions for localization in the two DNA-containing organelles. Green/red fluorescent protein fusions of four of them were shown to be targeted to chloroplasts, where they colocalize with each other as well as with the plastid envelope DNA binding protein in structures corresponding to plastid nucleoids. For SWIB-6 and SWIB-4, a second localization in mitochondria and nucleus, respectively, could be observed. SWIB-4 has a histone H1 motif next to the SWIB domain and was shown to bind to DNA. Moreover, the recombinant SWIB-4 protein was shown to induce compaction and condensation of nucleoids and to functionally complement a mutant of Escherichia coli lacking the histone-like nucleoid structuring protein H-NS.
Institute of Botany, Christian-Albrechts-University of Kiel, 24098 Kiel, Germany.
Joanna
J
Melonek
Andrea
A
Matros
Mirl
M
Trösch
Hans-Peter
HP
Mock
Karin
K
Krupinska
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism; D002736:Chloroplasts / Q000235:genetics* / Q000378:metabolism; D032461:Chromosomes, Plant / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D015180:Electrophoresis, Gel, Two-Dimensional; D004926:Escherichia coli / Q000166:cytology / Q000235:genetics / Q000378:metabolism; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D010802:Phylogeny; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D017434:Protein Structure, Tertiary; D040901:Proteomics; D011993:Recombinant Fusion Proteins; D016415:Sequence Alignment; D018724:Spinacia oleracea / Q000166:cytology / Q000235:genetics* / Q000378:metabolism; D014026:Nicotiana / Q000166:cytology / Q000235:genetics / Q000378:metabolism; D000097573:Red Fluorescent Protein
D004268:DNA-Binding Proteins; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; D000097573:Red Fluorescent Protein