  The interactions between proteins, DNA, and RNA in living cells constitute
molecular networks that govern various cellular functions. To investigate the
global dynamical properties and stabilities of such networks, we studied the
cell-cycle regulatory network of the budding yeast. With the use of a simple
dynamical model, it was demonstrated that the cell-cycle network is extremely
stable and robust for its function. The biological stationary state--the G1
state--is a global attractor of the dynamics. The biological pathway--the
cell-cycle sequence of protein states--is a globally attracting trajectory of
the dynamics. These properties are largely preserved with respect to small
perturbations to the network. These results suggest that cellular regulatory
networks are robustly designed for their functions.
