Transcriptional Activation by Simian Virus 40 Large T Antigen: Interactions with Multiple Components of the Transcription Complex

Abstract

Simian virus 40 (SV40) large T antigen is a potent transcriptional activator of both viral and cellular promoters. Within the SV40 late promoter, a specific upstream element necessary for T-antigen transcriptional activation is the binding site for transcription-enhancing factor 1 (TEF-1). The promoter structure necessary for T-antigen-mediated transcriptional activation appears to be simple. For example, a promoter consisting of upstream TEF-1 binding sites (or other factor-binding sites) and a downstream TATA or initiator element is efficiently activated. It has been demonstrated that transcriptional activation by T antigen does not require direct binding to the DNA; thus, the most direct effect that T antigen could have on these simple promoters would be through protein-protein interactions with either upstream-bound transcription factors, the basal transcription complex, or both. To determine whether such interactions occur, full-length T antigen or segments of it was fused to the glutathione-binding site (GST fusions) or to the Gal4 DNA-binding domain (amino acids 1 to 147) (Gal4 fusions). With the GST fusions, it was found that TEF-1 and the TATA-binding protein (TBP) bound different regions of T antigen. A GST fusion containing amino acids 5 to 172 (region T1) efficiently bound TBP. TEF-1 bound neither region T1 nor a region between amino acids 168 and 373 (region T2); however, it bound efficiently to the combined region (T5) containing amino acids 5 to 383.(ABSTRACT TRUNCATED AT 250 WORDS)

A geminivirus replication protein interacts with the retinoblastoma protein through a novel domain to determine symptoms and tissue specificity of infection in plants

“…To overcome this limitation, mammalian DNA tumor viruses encode proteins that interact with components of the host transcriptional apparatus and cell cycle regulatory network (Nevins, 1992). They target basal transcription factors (Gruda et al ., 1993), the histone transacetylase p300 (Eckner et al ., 1994), and the tumor suppressors, pRb (Dyson et al ., 1992) and p53 (Werness et al ., 1990). These protein interactions cause quiescent animal cells to re‐enter the cell division cycle and synthesize the enzymes necessary for viral DNA replication.…”

Chromatin structure and factor site occupancies in an in vivo-assembled transcription elongation complex

“…The open region contains binding sites for numerous trans-acting factors that stimulate transcription from the late promoter (6,7,(28)(29)(30)(44)(45)(46)(47)(48)(49). In order to gain insight into mechanisms by which trans-acting factors function, we determined the level of occupancy of several trans-acting factor binding sites in the VTC origin region.…”

“…It was found that T-antigen is absent from the origin site in the elongation complex, a finding that was inconsistent with certain models for the role of T-antigen in the control of transcription. This in turn spurred efforts to evolve alternative models for the participation of T-antigen in late transcription (6)(7)(8).…”

Novel Human TEF-1 Isoforms Exhibit Altered DNA Binding and Functional Properties

“…Overexpression of TEF-1 in a variety of cells resulted in squelching of transcriptional activity (2,7,8,24), suggesting that other limiting transcriptional co-activators are required for TEF-1 transactivation functions. We and others subsequently found that TEF-1 can interact with TBP (6,24,25), an essential component of the basal transcription machinery, and prevent TBP binding to the TATA box (24). These findings provide one mechanism by which TEF-1 may negatively regulate gene expression.…”

“…These homologues are derived from separate genes, and the individual products are expressed differentially in a variety of tissues (1)(2)(3)(4)(5). Initially TEF-1 was identified as a 53 kDa HeLa protein required for SV40 early gene transcription (1), which is mediated by TEF-1 binding to the GT-IIC and SphI/SphII enhansons associated with the SV40 early gene enhancer (2,6,7). Subsequent studies proved TEF-1 is a ubiquitous factor implicated in directing the expression of a wide variety of genes, including human papillomavirus-16 E6 and E7 oncogene transcription (8), murine cardiac and skeletal muscle-specific gene expression (9)(10)(11)(12)(13), and early gene expression in mouse development (14).…”