Adenovirus type 2 (Ad2) causes respiratory infections in humans, grows productively on human cell lines such as HeLa and KB, and can transform rat primary cell lines (Tooze 1973). The Ad2 virion consists of a linear duplex DNA chromosome 35,000 base pairs (bp) long (23 × 106 daltons) contained within an icosahedral capsid composed of at least ten different proteins. After penetration of the cell membrane, the viral DNA and several core proteins associated with it are transported to the nucleus, where early RNA transcription begins within 2 hours. About 8 hours after infection, viral DNA replication commences, reaching a maximum rate several hours later. Late transcription to produce messenger RNA (mRNA) for capsid and other virus-specific proteins begins after the onset of DNA replication and continues for about 2 days, when the infected cells die.