Topological basis of signal integration in the   transcriptional-regulatory network of the yeast, Saccharomyces cerevisiae
  BACKGROUND. Signal recognition and information processing is a fundamental cellular function, which in part involves comprehensive transcriptional regulatory (TR) mechanisms carried out in response to complex environmental signals in the context of the cell's own internal state. However, the network topological basis of developing such integrated responses remains poorly understood.   RESULTS. By studying the TR network of the yeast Saccharomyces cerevisiae we show that an intermediate layer of transcription factors naturally segregates into distinct subnetworks. In these topological units transcription factors are densely interlinked in a largely hierarchical manner and respond to external signals by utilizing a fraction of these subnets.   CONCLUSIONS. As transcriptional regulation represents the "slow" component of overall information processing, the identified topology suggests a model in which successive waves of transcriptional regulation originating from distinct fractions of the TR network control robust integrated responses to complex stimuli. 
Illes J. Farkas, Chuang Wu, Chakra Chennubhotla, Ivet Bahar, Zoltan N.   Oltvai