Biologists have long known that the activity of proteins inside of cells directs the expression of genes. What we generally lack is a quantitative understanding of these regulatory interactions. For example, how does the amount of a regulatory protein determine the nature and extent of regulatory interactions? In this talk, Dr. Stoebel will explore answers to this question by studying how the regulatory protein RpoS, found in the model bacterium Escherichia coli, influences the transcription of all genes in the genome. Whole genome-studies reveal that the shape of the relationship between RpoS levels and level of transcription varies dramatically between different RpoS-regulated genes. Experiments with specific promoters demonstrate that the sequence of the core promoter does not determine the shape of this relationship. Rather, the binding of other transcription factors appears to modulate the relationship between RpoS and levels of transcription. The talk will conclude with thoughts about what can be learned from this more nuanced understanding of a regulatory network.