The Myc/Max/Mad network and the transcriptional control of cell behavior

The Myc/Max/Mad network comprises a group of transcription factors whose di stinct interactions result in gene-specific transcriptional activation or r epression. A great deal of research indicates that the functions of the net work play roles in cell proliferation, differentiation, and death. In this review we focus on the Myc and Mad protein families and attempt to relate t heir biological functions to their transcriptional activities and gene targ ets. Both Myc and Mad, as well as the more recently described Mnt and Mga p roteins, form heterodimers with Max, permitting binding to specific DNA seq uences. These DNA-bound heterodimers recruit coactivator or corepressor com plexes that generate alterations in chromatin structure, which in turn modu late transcription. Initial identification of target genes suggests that th e network regulates genes involved in the cell cycle, growth, life span, an d morphology. Because Myc and Mad proteins are expressed in response to div erse signaling pathways, the network can be viewed as a functional module w hich acts to convert environmental signals into specific gene-regulatory pr ograms.