ABSTRACT
This chapter discusses a way to detect building-block patterns in complex networks, called network motifs and examines the simplest network motif in transcription networks, negative autoregulation. It shows that this motif has useful functions: speeding up the response time of transcription interactions and stabilizing them against noise. The transcription network of Escherichia coli contains numerous patterns of nodes and arrows. A mutation that changes a single DNA letter in a promoter can abolish binding of a transcription factor and cause the loss of an arrow in the network. Negative autoregulation occurs when a transcription factor X represses its own transcription. Negative autoregulation can therefore use a strong promoter to give an initial fast production, and then use autorepression to stop production at the desired steady state. In addition to speeding the response time, negative autoregulation confers a second important benefit.
