  A model for the processive movement of dynein is presented based on
experimental observations available. In the model, the change from strong
microtubule-binding to weak binding of dynein is determined naturally by the
variation of the relative orientation between the two interacting surfaces of
the stalk tip and the microtubule as the stalk rotates from the ADP.Vi-state
orientation to the apo-state orientation. This means that the puzzling
communication from the ATP binding site in the globular head to the MT-binding
site in the tip of the stalk, which is prerequisite in the conventional model,
is not required. Using the present model, the previous experimental results,
such as (i) the step size of a dynein being an integer times of the period of
the MT lattice, (ii) the dependence of the step size on load, i.e., the step
size decreasing with the increase of load, and (iii) the stall force being
proportional to [ATP] at low [ATP] and becoming saturated at high [ATP], are
well explained.
