Atypical E2Fs: new players in the E2F transcription factor family.

As major regulators of the cell cycle, apoptosis and differentiation, E2F transcription factors have been studied extensively in a broad range of organisms. The recent identification of atypical E2F family members further expands our structural, functional and molecular view of the cellular E2F activity. Unlike other family members, atypical E2Fs have a duplicated DNA-binding domain and control gene expression without heterodimerization with dimerization partner proteins. Recently, knockout strategies in plants and mammals have pinpointed that atypical E2Fs have a crucial role in plant cell size control, endocycle regulation, proliferation and apoptotic response upon DNA stress. Their position at the crossroads of proliferation and DNA stress response marks these novel E2F proteins as interesting study objects in the field of tumor biology.