Analysis of DNA sequences which regulate the transcription of herpes simplex virus immediate early gene 3: DNA sequences required for enhancer-like activity and response to trans-activation by a virion polypeptide.

The far upstream region of herpes simplex virus (HSV) immediate early (IE) gene 3 has previously been shown to increase gene expression in an enhancer-like manner, and to contain sequences which respond to stimulation of transcription by a virion polypeptide, Vmw65. To analyse the specific DNA sequences which mediate these functions, sequential deletions from each end of the far upstream region were made. The effects of the deletions on transcription in the absence or presence of the Vmw65 were measured by use of a transient expression assay. The enhancer-like activity was due to three separable elements, whereas two additional DNA regions were involved in the response to Vmw65. One of the responding elements corresponded to an AT-rich consensus (TAATGARATTC, where R = purine) present in all IE gene far upstream regions, and the other was a GA-rich sequence also present in IE genes 2 and 4/5. The TAATGARATTC element could mediate responsiveness to Vmw65 but it was fully active only in the presence of the GA-rich element. The GA-rich element was unable to confer a strong response alone but could activate an otherwise nonfunctional homologue of TAATGARATTC.