A conserved region of unknown function participates in the recognition of E2F family members by the adenovirus E4 ORF 6/7 protein.

E2F DNA-binding activity in vivo is due to heterodimer formation between members of the E2F and DP transcription factor families. The ability of these heterodimers to serve as transcriptional regulators is modulated by complex formation with additional proteins such as the products of the retinoblastoma gene and the adenovirus E4 ORF 6/7. Each of the E2F family members cloned to date contains a highly conserved region of unknown function, termed the marked box, which lies between their DNA binding and transactivation domains. Mutational analysis showed that the marked box contributed to the recognition of E2F family members by the E4 ORF 6/7 protein in vitro and in vivo.