An adenovirus mutant unable to express VAI RNA displays different growth responses and sensitivity to interferon in various host cell lines.

The VAI RNA of adenovirus is a small, RNA polymerase III-transcribed species required for the efficient translation of host cell and viral mRNAs late after infection. VAI RNA prevented activation of the interferon-induced P1/eIF-2 alpha kinase. In its absence the kinase was activated, eIF-2 alpha was phosphorylated, and translational initiation was inhibited. H5dl331 (dl331), a mutant which cannot express VAI RNA, grew poorly in 293 cells but generated wild-type yields in KB cells. The growth phenotype of the mutant appeared to correlate with the kinetics of kinase induction and activation. Active kinase appeared more rapidly in cell extracts prepared from infected 293 cells, in which dl331 grew poorly, than in extracts of KB cells, in which the mutant grew well. However, when kinase was induced in KB cells by interferon treatment and then activated subsequent to dl331 infection, viral protein synthesis was less severely inhibited than in interferon-treated 293 cells. Thus, activated kinase per se is insufficient to severely inhibit dl331 protein synthesis in KB cells.