Expression from a human cytomegalovirus early promoter (E1.7) has been shown to be activated in trans by the IE2 gene product. Although the IE1 gene product alone had no effect on this early viral promoter, maximal early promoter activity was detected when both IE1 and IE2 gene products were present. The IE1 protein from cytomegalovirus is also known as UL123.
Jiyao W et al.(2023). "The conserved domain database in 2023.",