  Intracellular transport is mediated by molecular motors that pull cargos
along cytoskeletal filaments. Many cargos move bidirectionally and are
transported by two teams of motors which move into opposite directions along
the filament. We have recently introduced a stochastic tug-of-war model for
this situation. This model describes the motion of the cargo as a Markov
process on a two-dimensional state space defined by the numbers of active plus
and active minus motors. In spite of its simplicity, this tug-of-war model
leads to a complex dependence of the cargo motility on the motor parameters. We
present new numerical results for the dependence on the number of involved
motors. In addition, we derive a simple and intuitive sharp maxima
approximation, from which one obtains the cargo motility state from only four
simple inequalities. This approach provides a fast and reliable method to
determine the cargo motility for a given experimental system.
