In mammals the E2F family is composed of eight E2F proteins, E2F1 through 8 and three DP proteins, DP1, DP2, and DP4. In Drosophila it consists of two E2Fs, dE2F1, dE2F2, and one DP protein, dDP. The eight mammalian E2F proteins can be divided into three groups: activating E2Fs (E2F1, E2F2, and E2F3), repressive E2Fs (E2F4 and E2F5), and Rb independent E2Fs (E2F6, E2F7, and E2F8). The mammalian activating E2Fs interact only with Rb. Similarly, the Drosophila activating E2F, dE2F1, interacts only with RBF. The mammalian repressive E2Fs interact with p107 and p130. In addition, E2F4 can also interact with Rb protein. Similarly, the Drosophila repressive E2F, dE2F2, interacts with both RBF and RBF2.