Immediate early (EI) protein that functions as a transcriptional regulator of cellular and viral mRNAs mainly by interacting with several general transcription factors thereby disorganizing the preinitiation complex at certain promoters. May additionally help to regulate levels of histones in virus-infected cells by interacting with host ASF1. By inhibiting host transcriptional program, IE63 plays a major role in the ability of VZV to overcome the innate immune response to the virus (By similarity). Interacts with IE62; this interaction modulates the function of IE62. Interacts with several components of host pre-initiation complex including GTF2E1, GTF2H2 and POLR2A; these interactions lead to repression of gene transcription. Interacts with host ASF1; altering its ability to bind histones. During the first stage of infection, IE63 is mostly expressed in the nucleus and also slightly in the cytoplasm, and during latency, IE63 localizes in the cytoplasm quite exclusively. Phosphorylated in vitro by host and by protein kinase ORF47. Belongs to the herpesviridae ICP22 family.