Changes in cell behavior induced by extracellular signaling molecules such as growth factors and cytokines require execution of a complex program of transcriptional events. While the route followed by the intracellular signal from the cell membrane to its transcription factor targets can be traced in an increasing number of cases, how the specificity of the transcriptional response of the cell to different stimuli is determined is much less clear. However, it is possible to understand at least in principle how different stimuli can activate the same signal pathway yet activate different genes and how small differences in signal strength can generate qualitative differences in gene expression.

In this review we shall concentrate on transcriptional responses to cell surface receptor-activated signaling pathways; however, much of our discussion is also applicable to signals induced by environmental stresses or to extracellular …