Figure 6

Pae χψ binds to an SSB/ssDNA complex with higher affinity than Eco χψ. ( A ) Pae χψ or ( B ) Eco χψ were titrated to 0.35 μM of their respective SSB in absence (diamonds) or presence (triangles) of 12.3 μM poly(dT), in low salt buffer (50000 rpm or 22000 rpm in the absence or presence of poly(dT), respectively, 20°C, λ = 230 nm). The lines represent theoretical binding isotherms calculated for a simple interaction model of n molecules of χψ with one SSB tetramer using the following parameters: ( A ) n = 2.2, K = 5 × 10⁷ M^-1 and ( B ) n = 3, K = 6 × 10⁶ M^-1. The affinity of Pae χψ for the SSB/ssDNA complex is so high that only a lower limit of the binding constant can be given.