title: Characterization of a mitochondrially targeted single-stranded DNA-binding protein in Arabidopsis thaliana.
abstract: A gene encoding a predicted mitochondrially targeted single-stranded DNA binding protein (mtSSB) was identified in the Arabidopsis thaliana genome sequence. This gene (At4g11060) codes for a protein of 201 amino acids, including a 28-residue putative mitochondrial targeting transit peptide. Protein sequence alignment shows high similarity between the mtSSB protein and single-stranded DNA binding proteins (SSB) from bacteria, including residues conserved for SSB function. Phylogenetic analysis indicates a close relationship between this protein and other mitochondrially targeted SSB proteins. The predicted targeting sequence was fused with the GFP coding region, and the organellar localization of the expressed fusion protein was determined. Specific targeting to mitochondria was observed in in-vitro import experiments and by transient expression of a GFP fusion construct in Arabidopsis leaves after microprojectile bombardment. The mature mtSSB coding region was overexpressed in Escherichia coli and the protein was purified for biochemical characterization. The purified protein binds single-stranded, but not double-stranded, DNA. MtSSB stimulates the homologous strand-exchange activity of E. coli RecA. These results indicate that mtSSB is a functional homologue of the E. coli SSB, and that it may play a role in mitochondrial DNA recombination.
authors.affiliation: Department of Microbiology and Molecular Biology, Brigham Young University, 775 WIDB, Provo, UT, 84602, USA.
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Edmondson
authors.forename: Daqing
authors.initials: D
authors.lastname: Song
authors.forename: Luis A
authors.initials: LA
authors.lastname: Alvarez
authors.forename: Melisa K
authors.initials: MK
authors.lastname: Wall
authors.forename: David
authors.initials: D
authors.lastname: Almond
authors.forename: David A
authors.initials: DA
authors.lastname: McClellan
authors.forename: Anthony
authors.initials: A
authors.lastname: Maxwell
authors.forename: Brent L
authors.initials: BL
authors.lastname: Nielsen
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics*; D019470:Biolistics; D019295:Computational Biology; D004268:DNA-Binding Proteins / Q000235:genetics*; D004926:Escherichia coli; D040461:Gene Components; D049452:Green Fluorescent Proteins; D016013:Likelihood Functions; D008928:Mitochondria / Q000378:metabolism*; D008957:Models, Genetic; D008969:Molecular Sequence Data; D010802:Phylogeny; D011938:Rec A Recombinases / Q000378:metabolism; D016415:Sequence Alignment; D020539:Sequence Analysis, Protein
chemical_list: D004268:DNA-Binding Proteins; D049452:Green Fluorescent Proteins; D011938:Rec A Recombinases
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