title: Structure-function relationships of two paralogous single-stranded DNA-binding proteins from Streptomyces coelicolor: implication of SsbB in chromosome segregation during sporulation.
abstract: The linear chromosome of Streptomyces coelicolor contains two paralogous ssb genes, ssbA and ssbB. Following mutational analysis, we concluded that ssbA is essential, whereas ssbB plays a key role in chromosome segregation during sporulation. In the ssbB mutant, ∼30% of spores lacked DNA. The two ssb genes were expressed differently; in minimal medium, gene expression was prolonged for both genes and significantly upregulated for ssbB. The ssbA gene is transcribed as part of a polycistronic mRNA from two initiation sites, 163 bp and 75 bp upstream of the rpsF translational start codon. The ssbB gene is transcribed as a monocistronic mRNA, from an unusual promoter region, 73 bp upstream of the AUG codon. Distinctive DNA-binding affinities of single-stranded DNA-binding proteins monitored by tryptophan fluorescent quenching and electrophoretic mobility shift were observed. The crystal structure of SsbB at 1.7 Å resolution revealed a common OB-fold, lack of the clamp-like structure conserved in SsbA and previously unpublished S-S bridges between the A/B and C/D subunits. This is the first report of the determination of paralogous single-stranded DNA-binding protein structures from the same organism. Phylogenetic analysis revealed frequent duplication of ssb genes in Actinobacteria, whereas their strong retention suggests that they are involved in important cellular functions.
authors: Division of Molecular Biology, Rudjer Boskovic Institute, Zagreb 10002, Croatia.
authors: Tina
authors: T
authors: Paradzik
authors: Nives
authors: N
authors: Ivic
authors: Zelimira
authors: Z
authors: Filic
authors: Babu A
authors: BA
authors: Manjasetty
authors: Paul
authors: P
authors: Herron
authors: Marija
authors: M
authors: Luic
authors: Dusica
authors: D
authors: Vujaklija
mesh_terms: D039903:Actinobacteria / Q000145:classification / Q000235:genetics; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D001483:Base Sequence; D020090:Chromosome Segregation; D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010802:Phylogeny; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D013171:Spores, Bacterial / Q000235:genetics; D048372:Streptomyces coelicolor / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D013329:Structure-Activity Relationship; D024363:Transcription Initiation Site
chemical_list: D001426:Bacterial Proteins; D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins
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