Growth Regulation by the E2F and DP Transcription Factor Families

What we know about E2F transcriptional activity has been derived from several lines of investigation. Each line of study gives us greater insight into understanding the function of E2F transcriptional activity in growth control. In vivo and in vitro, E2F transcriptional activity appears to be complex, often capable of completely opposing actions. The basis for positive and negative action at many levels appears to be the ability of E2F transcriptional activity to transactivate and repress gene expression, which both require the same initial step, i.e., recognition of target DNA. When bound to the retinoblastoma tumor suppressor (pRB) or other pRB family members, E2F functions as a repressor, and when "free" of pRB family interaction, E2F functions as an activator. It is this positive and negative, up and down nature of E2F activity that fascinates so many investigators.