Analysis of Gene Expression Data 10.1 Protein Interaction Networks 10.2 High-throughput Technologies for Measuring Protein- Protein Interactions 10.2.1 Yeast Two-hybrid 10.2.2 Protein Coimmunoprecipitation (coip)

In the past we have discussed different types of biological networks. For example, in the context of gene expression we discussed networks in which each node represents a gene and an edge represents a similarity of gene expression profiles. In this lecture, protein interaction networks will be discussed. Protein interaction networks are graphs in which each node represents a protein, and an edge between two nodes represents an evidence for the presence of a physical interaction between the two proteins. A small subset of such a network can be seen in Figure 10.1. For example, such a physical interaction can be a kinase protein which phosphorylates another protein. The network does not contain information about the nature of the interaction (activation, de-activation, two proteins which participate in the same complex, etc.). The use of protein interaction networks has recently expanded due to the development of high-throughput technologies measuring these interactions, and the availability of large data sources containing interaction evidence for different species.