  Understanding design principles of molecular interaction networks is an
important goal of molecular systems biology. Some insights have been gained
into features of their network topology through the discovery of graph
theoretic patterns that constrain network dynamics. This paper contributes to
the identification of patterns in the mechanisms that govern network dynamics.
The control of nodes in gene regulatory, signaling, and metabolic networks is
governed by a variety of biochemical mechanisms, with inputs from other network
nodes that act additively or synergistically. This paper focuses on a certain
type of logical rule that appears frequently as a regulatory pattern. Within
the context of the multistate discrete model paradigm, a rule type is
introduced that reduces to the concept of nested canalyzing function in the
Boolean network case. It is shown that networks that employ this type of
multivalued logic exhibit more robust dynamics than random networks, with few
attractors and short limit cycles. It is also shown that the majority of
regulatory functions in many published models of gene regulatory and signaling
networks are nested canalyzing.
