HCMV replicates within infected endothelial cells at a slow rate, taking about 5 days in cell culture. Like other herpesviruses, HCMV expresses genes in a temporally controlled manner. Immediate early genes (0–4 hours after infection) are involved in the regulation of transcription, followed by early genes (4–48 hours after infection) which are involved in viral DNA replication and further transcriptional regulation. Late genes are expressed during the remainder of infection up to viral egress and typically code for structural proteins. While HCMV encodes for its own functional DNA polymerase, the virus makes use of the host RNA polymerase for the transcription of all of its genes.