RB1 and neoplasm: The adenoviral E1A and E1B proteins are necessary for efficient viral replication in normal cells, where E1A binds retinoblastoma protein (pRb), releasing transcription factor E2F, leading to efficient viral DNA replication, and E1B-55 K mediates efficient viral mRNA transport; the former function is partially complemented in tumor cells that lack pRB, and the latter function is also complemented in some tumor cells, although the molecular mechanism has not been fully understood.