Anchoring a vaccinia virus promoter in the nucleus prevents its trans-activation by viral infection.

The vaccinia virus 7.5 kDa constitutive promoter, when fused to a reporter gene and recombined into the genome of L cells, is not activatable upon subsequent infection with vaccinia virus. However, the same promoter is actively transcribed during transient cytoplasmic transfection procedures or within the context of the viral genome. This suggests that the intact vaccinia transcriptional machinery either does not enter the nucleus or, if it does, is unable to interact with cellular chromatin.