(A) Yeast SH3 domain protein-protein interaction network predicted using phage display selected peptides. 394 interactions and 206 proteins are shown; a network with each gene name labelled is included in the supplementary material (7). The proteins are colored according to their k-core value (6-core = black, 5-core = cyan, 4-core = blue, 3-core = red, 2- core = green, 1-core = yellow), identifying subsets of interconnected proteins in which each protein has at least k interactions. By definition, lower core numbers encompass all higher core numbers (e.g. a 4-core includes all the nodes in the 4-core, 5-core and 6-core). The interactions of the 6-core subgraph are highlighted in red. (B) The 6-core subgraph derived from the phage display protein-protein interaction network, expanded to allow identification of individual proteins. The 6-core subset contains 8 SH3 domain proteins (Abp1, Bbc1, Rvs167, Sla1, Yfr024c, Ysc84, Ypr154w, and Ygr136w) and 5 proteins predicted to bind at least 6 different SH3 domains (Las17, Acf2, Ypr171w, Ygl060w, and Ynl094w).