Fig. 6
a Method for calculating the compaction force (Fc) induced by protein-DNA interactions. Inset shows stretch (solid lines) and return (dashed lines) curves for dsDNA in the absence of protein and in the presence of near saturated (30 nM) HIV-1 NC protein. Fc is calculated in the low force-extension regime denoted within the gray box in the inset and magnified in the main figure. The DNA only extension curve is fit to the WLC model (Additional file 4: Eq. 1). The force difference (Fc) between the return curve in the presence of high protein concentration and the DNA only stretching curve is averaged over measured extensions <0.31 nm/bp to obtain Fc. b Fc for SIV NC and HIV-1 NC for concentrations of 30 nM and 60 nM. Error bars are standard errors for three or more measurements