Figure 3

Pae χψ and Eco χψ bind with similar affinities to their cognate SSB proteins. 6 μM SSB was sedimented in the analytical ultracentrifuge in high salt buffer, at 50000 rpm and 20°C (λ = 280 nm) in the presence of increasing concentrations of χψ. Binding isotherms for the interactions of χψ with SSB for the proteins of P. aeruginosa (diamonds) and E. coli (triangles) were obtained by analysis of the c(s) distributions (see Methods section). The solid lines represent theoretical binding isotherms calculated for a simple interaction model of n molecules of χψ with one SSB tetramer using the following parameters: Pae n = 2.2, K = 1.3 × 10⁵ M^-1; Eco n = 3.8, K = 1.8 × 10⁵ M^-1.