title: Characterization of single-stranded DNA-binding proteins from Mycobacteria. The carboxyl-terminal of domain of SSB is essential for stable association with its cognate RecA protein.
abstract: Single-stranded DNA-binding proteins (SSB) play an important role in most aspects of DNA metabolism including DNA replication, repair, and recombination. We report here the identification and characterization of SSB proteins of Mycobacterium smegmatis and Mycobacterium tuberculosis. Sequence comparison of M. smegmatis SSB revealed that it is homologous to M. tuberculosis SSB, except for a small spacer connecting the larger amino-terminal domain with the extreme carboxyl-terminal tail. The purified SSB proteins of mycobacteria bound single-stranded DNA with high affinity, and the association and dissociation constants were similar to that of the prototype SSB. The proteolytic signatures of free and bound forms of SSB proteins disclosed that DNA binding was associated with structural changes at the carboxyl-terminal domain. Significantly, SSB proteins from mycobacteria displayed high affinity for cognate RecA, whereas Escherichia coli SSB did not under comparable experimental conditions. Accordingly, SSB and RecA were coimmunoprecipitated from cell lysates, further supporting an interaction between these proteins in vivo. The carboxyl-terminal domain of M. smegmatis SSB, which is not essential for interaction with ssDNA, is the site of binding of its cognate RecA. These studies provide the first evidence for stable association of eubacterial SSB proteins with their cognate RecA, suggesting that these two proteins might function together during DNA repair and/or recombination.
authors.affiliation: Department of Biochemistry, Indian Institute of Science, Bangalore 560 012, India.
authors.forename: M S
authors.initials: MS
authors.lastname: Reddy
authors.forename: N
authors.initials: N
authors.lastname: Guhan
authors.forename: K
authors.initials: K
authors.lastname: Muniyappa
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D002850:Chromatography, Gel; D003001:Cloning, Molecular; D004247:DNA; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D024202:Electrophoretic Mobility Shift Assay; D006868:Hydrolysis; D008969:Molecular Sequence Data; D009161:Mycobacterium / Q000378:metabolism*; D011485:Protein Binding; D011995:Recombination, Genetic; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity
chemical_list: D004268:DNA-Binding Proteins; D004247:DNA