The adenovirus early region 1A (E1A) proteins associate with several cellular proteins in adenovirus infected or transformed cells. Recently, two of the cellular proteins that bind to E1A encoded proteins have been identified. p105 has been shown to be the product of the retinoblastoma tumor suppressing gene. p60 has been shown to be a human cyclin A. Previously studies have shown that E1A protein sequences encoded by conserved domains 1 and 2 are required for interactions with the retinoblastoma protein (pRB). We have demonstrated here that amino acids 30 to 60 and 121 to 127 within the E1A proteins are required for interaction with p60/cyclin A. These are the same sites within conserved domains 1 and 2 that are required for E1A protein association with pRB. However, the association of p60/cyclin A does not appear to require pRB. We also demonstrate that another cellular protein, 130K, interacts with E1A at essentially the same sites. It is interesting that mutations in these regions destroy the ability of E1A to function as an oncogene, thereby raising the possibility that interaction with several different cellular proteins may be needed for transformation by E1A.