The PAS superfamily: Sensors of environmental and developmental signals

Over the past decade, PAS domains have been identified in dozens of signal transduction molecules and various forms have been found in animals, plants , and prokaryotes. In this review, we summarize this rapidly expanding rese arch area by providing a detailed description of three signal transduction pathways that utilize PAS protein heterodimers to drive their transcription al output. It is hoped that these model pathways can provide a framework fo r use in understanding the biology of the less well-understood members of t his emerging superfamily, as well as of those to be characterized in the da ys to come. We use this review to develop the idea that most eukaryotic PAS proteins can be classified by functional similarities, as well as by predi cted phylogenetic relationships. We focus on the alpha-class proteins, whic h often act as sensors of environmental signals, and the beta-class protein s, which typically act as broad-spectrum partners that target these heterod imers to their genomic targets.