Cycloheximide stimulates early adenovirus transcription if early gene expression is allowed before treatment.

The inhibition of protein synthesis by cycloheximide markedly stimulated adenovirus 2 early transcription (assayed in vivo and in vitro in nuclei) when the drug was added 3 h after infection of HeLa cells. The stimulation was not uniform but ranged from three- to eightfold for region 1A to 10- to 30-fold for region 2 of the adenovirus genome. The increase was complete by about 60 min after treatment. The stimulation reversed rapidly after cycloheximide was removed. Treatment with cycloheximide either before infection with wild-type adenovirus type 5 or at 3 h after infection with dl312, a mutant which fails to express early gene products in HeLa cells, both resulted in levels of transcription at or substantially below the control (infection with wild-type adenovirus without treatment). Therefore we conclude that cycloheximide treatment and previous early gene expression interact to yield the maximum levels of transcription.