E2Fs have been implicated in regulating at least three critical aspects of cell growth: cell cycle entry, differentiation and apoptosis. At present, the human E2F family is known to contain five members, E2F1 through E2F5. These E2F family members bind DNA as heterodimers with members of the DP family of polypeptides. DP family contains at least two members, DP1 and 2. Structurally, DP1 and 2 are relatively conserved, yet their expression appears to be tissue specific. The interaction between members of the E2F and the DP families is mediated, at least in part, by a leucine repeat, which is weakly conserved between the two families.