The immediate-early protein ICP4 (infected-cell polypeptide 4) is required for efficient transcription of early and late viral genes and is thus essential for productive infection. ICP4 is a large phosphoprotein that binds DNA in a sequence specific manner as a homodimer. ICP4 represses transcription from LAT, ICP4 and ORF-P that have high-affinity a ICP4 binding site that spans the transcription initiation site. ICP4 proteins have two highly conserved regions, this family contains the C-terminal region that probably acts as an enhancer for the N-terminal region.
Jiyao W et al.(2023). "The conserved domain database in 2023.",