Network analysis became a powerful tool giving new insights to the understanding of cellular behavior . Heat shock , the archetype of stress responses, is a well-characterized and simple model of cellular dynamics. S. cerevisiae is an appropriate URLanism, since both its protein-protein interaction network (interactome) and stress response at the gene expression level have been well characterized. However, the analysis of the URLanization of the yeast interactome during stress has not been investigated yet. Changes of interaction-weights of yeast interactome were calculated from the changes of mRNA expression levels . Heat shock induced a significant decrease in both the overlaps and connections of yeast interactome modules. In agreement with this the weighted diameter of the yeast interactome had a 4.9-fold increase in heat shock. Several key proteins of the heat shock response became centers of heat shock-induced local communities, as well as bridges providing a residual connection of modules after heat shock. The observed changes resemble to a  stratus-cumulus  type transition of the interactome structure, since the unstressed yeast interactome had a globally URLanization, similar to that of stratus clouds, whereas the heat shocked interactome had a URLanization, similar to that of cumulus clouds. Our results showed that heat shock induces a partial disintegration of the URLanization of the yeast interactome. This change may be rather general occurring in many types of stresses. Moreover, other complex systems, such as single proteins, social networks and ecosystems may also decrease their inter-modular links, thus develop more compact modules, and display a partial disintegration of their global structure in the initial phase of crisis. Thus, our work may provide a model of a general, system-level adaptation mechanism to environmental changes.
Network analysis became a powerful tool in recent years . Heat shock is a well-characterized model of cellular dynamics. S. cerevisiae is an appropriate URLanism, since both its protein-protein interaction network (interactome) and stress response at the gene expression level have been well characterized. However, the analysis of the URLanization of the yeast interactome during stress has not been investigated yet. We calculated the changes of the interaction-weights of the yeast interactome from the changes of mRNA expression levels upon heat shock. The major finding of our study is that heat shock induced a significant decrease in both the overlaps and connections of yeast interactome modules. In agreement with this the weighted diameter of the yeast interactome had a 4.9-fold increase in heat shock. Several key proteins of the heat shock response became centers of heat shock-induced local communities, as well as bridges providing a residual connection of modules after heat shock. The observed changes resemble to a " stratus-cumulus " type transition of the interactome structure, since the unstressed yeast interactome had a globally URLanization, similar to that of stratus clouds, whereas the heat shocked interactome had a URLanization, similar to that of cumulus clouds. Our results showed that heat shock induces a partial disintegration of the URLanization of the yeast interactome. This change may be rather general occurring in many types of stresses. Moreover, other complex systems, such as single proteins, social networks and ecosystems may also decrease their inter-modular links, thus develop more compact modules, and display a partial disintegration of their global structure in the initial phase of crisis. Thus, our work may provide a model of a general, system-level adaptation mechanism to environmental changes.
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