FIGURE 3.

Plots of zippered and unzippered stationary probability densities (in arbitrary units) versus the reduced interval [−d, d] (see Neck Linkers and the Coiled-Coil Neck and Eq. 11), for the case example in Biasing Mechanism that ignores the effects of weak state unbinding. The use of the reduced interval, which subtracts the coiled-coil extension, hides the fact that zippering is a small change (∼2 nm) compared to the distance traveled by one head (∼16 nm). Zippering probabilities, e.g., Eq. 3, are not represented in these plots. As discussed in Basic Biasing Mechanism and the Heuristic Model of Bias, the small and decreasing tails of the distribution are responsible for the generation of large biases. Apparent in these plots are the competing influences of zippering, which shifts the density toward the plus-end, and of loads, which shifts the density toward the minus-end. Stall occurs when all these effects balance one another. The inclusion of weak state unbinding in the model preserves many of the features presented here.