FIGURE 16.

Histogram of the α, α′-angles of segments a, a′ in the open (top) and closed complex (bottom) for low (up to 40 pN) and high external forces (40 pN and up). Both run I and II were used for f < 20 pN. Forces larger than 40 pN shift the angle distribution by 10°; of particular interest is the orientation α′ of a′, because this segment is the one opposite the incoming nucleotide. It is possible that forces in this range change the specificity of interactions with the correct nucleotide and could trigger exonucleolysis.