Human cytomegalovirus IE86 protein interacts with promoter-bound TATA-binding protein via a specific region distinct from the autorepression domain

The major immediate-early gene of human cytomegalovirus encodes several isoforms of an immediate-early protein which has distinct transcriptional regulatory properties. The IE86 isoform autorepresses the major immediate-early promoter by directly binding the cis repression signal element located between the TATA box and the mRNA cap site. In addition to this activity, IE86 stimulates other viral and cellular promoters. One mechanism by which eukaryotic regulatory proteins are thought to stimulate transcription is by contacting one or more general transcription factors. We show that the IE86 protein physically interacts with the DNA-binding subunit (TATA-binding protein) human transcription factor IID via the TATA-binding protein-contacting domain in the N terminus of IE86. In a mobility shift assay, IE86 was also observed to stabilize the binding of TATA-binding protein to promoter DNA. The domains within IE86 responsible for mediating transactivation and repression functioned independently. These experiments thus demonstrate the elegant ability of human cytomegalovirus to join different protein domains to produce distinct multifunctional proteins.