The pp28 protein of HCMV is a 190-amino-acid myristylated phosphoprotein that is expressed as a true late protein, i.e., it is synthesized only after the onset of viral DNA replication. The pp28 protein is encoded by UL99, the last open reading frame positioned within a family of 3-coterminal transcripts that share the same polyadenylation site. It is one of the most abundant constituents of the tegument layer and is highly immunogenic.