Transcriptional activation by the human cytomegalovirus immediate-early proteins: requirements for simple promoter structures and interactions with multiple components of the transcription complex

Abstract

We have utilized a number of well-defined, simple, synthetic promoters (upstream factor binding sites and TATA elements) to analyze the activation mechanisms of the human cytomegalovirus immediate-early (IE) proteins. We found that the 86-kDa IE protein (known as IEP86, IE2,g5aa, or ppUL122a) can recognize and activate a variety of simple promoters, in agreement with the observation that it is a promiscuous activator. However, in the comparison of otherwise identical promoters IEP86 does have preferences for specific TATA elements (hsp70 > adenovirus E2 > simian virus 40 early) and specific upstream transcription factor binding sites (CAAT > SPI Tef-1 > ATF; no activation with AP1 or OCT). In contrast, the 72-kDa IE protein (known as IEP72, IE1491aa, or ppUL123) alone did not significantly activate the simple promoters under our experimental conditions. However, each promoter activated by IEP86 was synergistically affected by the addition of IEP72. In addition, the 55-kDa IE protein (IEP55, a splice variant form of IE2, IE2425aa, or ppUL122b) repeatedly had a negative effect, downregulating the activation of promoters caused by IEP86 and the synergy of IEP86 and IEP72. We show that the ability of IEP86 to activate many simple promoters correlates not only with its previously described ability to interact with the TATA-binding protein (TBP) (B. A.

The major transcriptional transactivation domain of simian virus 40 large T antigen associates nonconcurrently with multiple components of the transcriptional preinitiation complex

“…Bovine papillomavirus type 1 E2 proteins both bind directly to TFIID and TFIIB and compete with VP16 for factors important for transactivation in vivo (47). The human cytomegalovirus 86K immediateearly 2 protein binds to TBP, TFIIB (9), and at least two other transcription factors (38). The HBx protein of human hepatitis B virus has been shown to interact with both TBP (46) and a subunit of RNA polymerases (10).…”

Binding of cellular repressor protein or the IE2 protein to a cis-acting negative regulatory element upstream of a human cytomegalovirus early promoter

“…In contrast, when the UL4 promoter had either 220 or 2,200 bp upstream, the basal activity was still low, but the viral IE2 protein enhanced transcription from the promoter 6-to 50-fold, respectively (23,38). We suggested that one effect of the IE2 protein may be mediated by the negation of a negative regulatory region upstream of the CCAAT box dyad symmetry as well as by direct interaction with TFIID (23) or other eucaryotic transcription factors (36).…”

“…Like other viral transactivators, such as adenovirus E1a, herpes simplex virus VP16 and ICP4, Epstein-Barr virus Zta, and human immunodeficiency virus Tat (3,21,25,26,33,40,53), the HCMV IE2 protein interacts with the TATA-box-binding protein (4,16,17,27,48). In vitro, the IE2 protein can interact with eucaryotic transcription factors such as Rb, SP-1, TEF-1, and TFIIB (4,15,36,48).…”

Early inhibitors of human cytomegalovirus: State-of-art and therapeutic perspectives

“…The transactivation properties of IE2-86 mainly rely on protein-protein interactions. In fact, IE2-86 interacts with several components of the basal transcription machinery, including TBP, TFIIB, and TAFII130-TAF4 (Caswell et al, 1993), showing by itself TAF-like functions (Lukac et al, 1994(Lukac et al, , 1997. Furthermore, both IE2-86 and IE1-72 attract histone acetylases to permit the activation of viral E promoters (Bryant et al, 2000;Nevels et al, 2004).…”