The single-stranded DNA-binding protein of Escherichia coli

Abstract

The single-stranded DNA-binding protein (SSB) of Escherichia coli is involved in all aspects of DNA metabolism: replication, repair, and recombination. In solution, the protein exists as a homotetramer of 18,843-kilodalton subunits. As it binds tightly and cooperatively to single-stranded DNA, it has become a prototypic model protein for studying protein-nucleic acid interactions. The sequences of the gene and protein are known, and the functional domains of subunit interaction, DNA binding, and protein-protein interactions have been probed by structure-function analyses of various mutations. The ssb gene has three promoters, one of which is inducible because it lies only two nucleotides from the LexA-binding site of the adjacent uvrA gene. Induction of the SOS response, however, does not lead to significant increases in SSB levels. The binding protein has several functions in DNA replication, including enhancement of helix destabilization by DNA helicases, prevention of reannealing of the single strands and protection from nuclease digestion, organization and stabilization of replication origins, primosome assembly, priming specificity, enhancement of replication fidelity, enhancement of polymerase processivity, and promotion of polymerase binding to the template. E. coli SSB is required for methyl-directed mismatch repair, induction of the SOS response, and recombinational repair. During recombination, SSB interacts with the RecBCD enzyme to find Chi sites, promotes binding of RecA protein, and promotes strand uptake.

Preliminary Characterization of Phage-like Particles from the Male-Killing MollicuteSpiroplasma poulsonii(an Endosymbiont ofDrosophila)

“…The 21.8 kbp phages of NSRO and Hydei and the 21 kbp phages of two non-Drosophila-associated strains (S. citri and S. mirum), are all reportedly circularly permuted and terminally redundant (Alivizatos et al 1982;Maniloff and Dybvig 1988), and thus, likely possess a headful packaging replication mechanism (Fujisawa and Morita 1997). The large phage-like terminase annotated in NSRO-P1 and NSRO-P2 could aid in the packing of viral dsDNA (Gual et al 2000), whereas the ssDNA binding protein and recombinases would most likely be involved in phage DNA replication (Meyer and Laine 1990). NSRO-P2 also possesses an ssDNA binding domain protein.…”

Regulation of Nearest-Neighbor Cooperative Binding of E. coli SSB Protein to DNA

“…Single-stranded (ss) DNA-binding proteins (SSBs) play essential roles in most aspects of DNA replication, recombination, and repair. They bind selectively and with high affinity to ssDNA intermediates formed transiently during genome maintenance, protecting them from degradation and inhibiting DNA secondary structures (1)(2)(3)(4). SSB pro-teins also serve as hubs for interactions with other proteins involved in genome maintenance.…”

Differential functional behavior of viral phi29, Nf and GA-1 SSB proteins

“…Single-stranded DNAbinding proteins (SSBs) destabilize double-stranded DNA (dsDNA) and bind without sequence specificity, but selectively and cooperatively, to single-stranded DNA (ssDNA) conferring a regular structure to it, which is recognized and exploited by a variety of enzymes involved in DNA replication, repair and recombination (2). Several cases have been reported of SSBs that stimulate their cognate DNA polymerase (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12). This modulation may be explained by the ability of the SSB to bind to ssDNA, melting out double-stranded regions by contiguous cooperative binding, but also by direct protein-protein interactions with proteins of the same replication system (3,9,(13)(14)(15)(16)(17).…”