  Understanding why some cellular components are conserved across species,
while others evolve rapidly is a key question of modern biology. Here we
demonstrate that in S. cerevisiae proteins organized in cohesive patterns of
interactions are conserved to a significantly higher degree than those that do
not participate in such motifs. We find that the conservation of proteins
within distinct topological motifs correlates with the motif's
inter-connectedness and function and also depends on the structure of the
overall interactome topology. These findings indicate that motifs may represent
evolutionary conserved topological units of cellular networks molded in
accordance with the specific biological function in which they participate.
