Our finding that Rbf1 can interact with chromosomal proteins like ORC regardless of E2F association gives fresh insight into the tumor suppressive properties of retinoblastoma proteins, since they may retain the potential to regulate cellular events, such as replication initiation, even while E2F binding to RB is inhibited by mutation, phosphorylation, or binding of viral oncoproteins [18]. This evidence concerns the gene RB1 and neoplasm.