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. 2008 Feb 14;36(6):1976–1989. doi: 10.1093/nar/gkm1174

Figure 1.

Figure 1.

PcrA binding to ssDNA substrates of different lengths measured with the fluorometric titration assay. A 50 nM PcrA was titrated with ssDNA and its intrinsic fluorescence was monitored as described in the Materials and Methods. (A) Intrinsic fluorescence of PcrA as a function of ssDNA concentration for the 16- and 26-nt ssDNA substrates. The ssDNA concentration of the titrant was 2380 nM (16 nt) or 950 nM (26 nt). The solid lines represented the best fits of the data to Equations (1) and (2) with Kd = 23.3 ± 2.1 nM, N = 2.0 ± 0.1 and Kd = 19.7 ± 3.3 nM, N = 2.6 ± 0.2 for the 16- and 26-nt substrates, respectively. (B) Stoichiometry of PcrA binding as a function of the ssDNA substrate length as obtained from analyses of the titration curves. The straight line was a linear fit of the data for ssDNA substrates longer than 16 nt, giving a slope of 0.107 ± 0.003 molecule/nt and thus a binding site size of 9.3 ± 0.3 nt. (C) The determined dissociation constant per site, Kd.