Figure 5. Topological features of protein-protein interaction sets in E. coli and S. cerevisiae.

In (A) we schematically illustrate interactions between co-regulated and co-regulating genes. In particular, co-regulated genes are considered a set of target genes that are controlled by a transcription factor. In turn, co-regulating genes refer to transcription factors that control the expression of the same genes. In (B) we calculated the number of interactions between co-regulated genes. In turn, we also calculated the enrichment of interactions between co-regulating genes in both E. coli and S. cerevisiae. As for their expected levels, we randomized the set of target genes of each transcription factor 10,000 times. While enrichments were significant in all datasets (P < 10⁻⁴) transcription factors tend to interact more frequently with each other than their target genes.