This is the coiled coil (CC) - marked box (MB) domain of E2F transcription factors. This domain forms a heterodimer with the corresponding domain of the DP transcription factor, the heterodimer binds the C-terminus of retinoblastoma protein [1].

1: Structure of the Rb C-terminal domain bound to E2F1-DP1: a mechanism for phosphorylation-induced E2F release. Rubin SM, Gall AL, Zheng N, Pavletich NP; Cell. 2005;123:1093-1106. PMID:16360038