FIGURE 4.

Transcriptional regulation of α-herpesviruses late gene expression. (A) Schematic representation of the initial step of formation of the Pre-Initiation Complex (PIC) on early and late α-herpesvirus promoters. (a) Early promoters contain either a TATA box, an initiator element (Inr) or both, associated with different cis-regulatory elements (cis-RE). TFIID (TBP associated with the TAFs) is stabilized on the promoter via its interaction with TFIIA. The structure of the viral chromatin is probably modified by the cis-regulatory factors to allow formation of the PIC and recruitment of ICP4. (b) Late promoters are composed of a TATA box associated with an Inr. The expression level of TFIIA is reduced within cells during the productive cycle. Recruitment of TFIID onto the late viral promoters is stabilized by ICP4. (B) Schematic representation of ICP4 functional domains. Gray boxes and text describe the various domains of ICP4 and their function. The functional domains of ICP4 include two transcriptional regulatory regions localized in the N- and C-terminal parts of the protein, respectively, separated by a region carrying a dimerization domain, a DNA-binding domain with a helix-turn-helix motif, and a nuclear localization sequence (NLS).