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Single-stranded DNA generated in the cell during DNA metabolism is stabilized and protected by binding of ssDNA-binding (SSB) proteins. Escherichia coli SSB, a representative homotetrameric SSB, binds to ssDNA by wrapping the DNA using its four subunits. However, such a tightly wrapped, high-affinity protein-DNA complex still needs to be removed or repositioned quickly for unhindered action of other proteins. Here we show, using single-molecule two- and three-colour fluorescence resonance energy transfer, that tetrameric SSB can spontaneously migrate along ssDNA. Diffusional migration of SSB helps in the local displacement of SSB by an elongating RecA filament. SSB diffusion also melts short DNA hairpins transiently and stimulates RecA filament elongation on DNA with secondary structure. This observation of diffusional movement of a protein on ssDNA introduces a new model for how an SSB protein can be redistributed, while remaining tightly bound to ssDNA during recombination and repair processes., The primary activity of SSB proteins in DNA metabolism is to bind preferentially to ssDNA with high affinity independently of sequence (1). However, SSB proteins also have a crucial role [...]

The negative enthalpy change (deltaH(sub obs)) is examined over a much wider temperature range and as a function of monovalent salt concentration and type for SSB binding to (dT)70 under solution conditions that favor the fully wrapped (SSB)65 complex using isothermal titration calorimetry. Over this wider temperature range, a strongly temperature-dependent negative heat capacity change (deltaC(sub p,obs) is observed.

Results show that Escherichia coli homotetrameric SSB protein is transferred from one single-stranded DNA molecule to another with the need for a protein intermediate. Data indicate that the rate of transfer is dependent on the amount of free DNA binding sites within the initital SSB tetramer-single-stranded DNA donor complex.

Research has been conducted on the homotetrameric Escherichia coli SSB protein's binding to the single-stranded oligodeoxynucleotides. The kinetic mechanism of this binding has been investigated under conditions allowing the fully wrapped ssDNA complex formation and the results are reported.

Salt concentration was shown to be significant in the stability and specificity of protein-nucleic acid interactions, as evidenced by the results of binding the tetrameric Escherichia coli single-stranded binding (SSB) protein to the poly(U) nucleic acid. Possible explanation for the event is the role of cations as they are bound to nucleic acids. Equilibrium association constant decreased with increased salt concentrations at all temperatures used when binding SSB proteins with the linear poly(U) nucleic acid.