The interplay between host and viral genes in adenovirus gene expression.

Only the left end of adenovirus DNA comprising the early E1A and E1B regions is required for transformation of rodent cells and for tumorigenicity in mice and rats. The E1A early region encodes a protein which probably indirectly through a cellular component controls mRNA expression from at least four other early regions at the transcriptional or post-transcriptional level. Viral early proteins also combine with or control the expression of the cellular transplantation antigens to prepare the host cell for tumor rejection or alternatively to suppress the cellular immune response. DNA replication of the viral genome requires three virus-coded proteins and two cellular proteins and is the first mammalian system where DNA can be efficiently replicated in an in vitro system. Adenovirus late expression is also subject to cellular controls since the virus uses the host cell machinery for transcription and splicing. A late translational control has also been identified which is mediated by a small virus coded RNA (VAI RNA) transcribed by the cellular polymerase III. The viral RNA is probably complexed with a cellular protein when exerting its effect. All these control mechanisms, involving both viral and cellular genes, are now being dissected, and several of the molecules involved have been identified.