Fig. 3.

Examples of discovered functional modules. (A) A module involved in cell-cycle regulation. This module consists of cyclins (CLB1-4 and CLN2) and cyclin-dependent kinases (CKS1 and CDC28) and a nuclear import protein (NIP29). Although they have many interactions, these proteins are not present in the cell at the same time. (B) Pheromone signal transduction pathway in the network of protein–protein interactions. This module includes several MAPK (mitogen-activated protein kinase) and MAPKK (mitogen-activated protein kinase kinase) kinases, as well as other proteins involved in signal transduction. These proteins do not form a single complex; rather, they interact in a specific order.