title: Upstream stimulatory factors binding to an E box motif in the R region of the bovine leukemia virus long terminal repeat stimulates viral gene expression.
abstract: The bovine leukemia virus (BLV) promoter is located in its 5'-long terminal repeat and is composed of the U3, R, and U5 regions. BLV transcription is regulated by cis-acting elements located in the U3 region, including three 21-bp enhancers required for transactivation of the BLV promoter by the virus-encoded transactivator Tax(BLV). In addition to the U3 cis-acting elements, both the R and U5 regions contain stimulatory sequences. To date, no transcription factor-binding site has been identified in the R region. Here sequence analysis of this region revealed the presence of a potential E box motif (5'-CACGTG-3'). By competition and supershift gel shift assays, we demonstrated that the basic helix-loop-helix transcription factors USF1 and USF2 specifically interacted with this R region E box motif. Mutations abolishing upstream stimulatory factor (USF) binding caused a reproducible decrease in basal or Tax-activated BLV promoter-driven gene expression in transient transfection assays of B-lymphoid cell lines. Cotransfection experiments showed that the USF1 and USF2a transactivators were able to act through the BLV R region E box. Taken together, these results physically and functionally characterize a USF-binding site in the R region of BLV. This E box motif located downstream of the transcription start site constitutes a new positive regulatory element involved in the transcriptional activity of the BLV promoter and could play an important role in virus replication.
authors.affiliation: Université Libre de Bruxelles, Institut de Biologie et de Médecine Moléculaires, Service de Chimie Biologique, Laboratoire de Virologie Moléculaire, Rue des Profs Jeener et Brachet 12, 6041 Gosselies, Belgium.
authors.forename: Claire
authors.initials: C
authors.lastname: Calomme
authors.forename: Thi Lien-Anh
authors.initials: TL
authors.lastname: Nguyen
authors.forename: Yvan
authors.initials: Y
authors.lastname: de Launoit
authors.forename: Veronique
authors.initials: V
authors.lastname: Kiermer
authors.forename: Louis
authors.initials: L
authors.lastname: Droogmans
authors.forename: Arsene
authors.initials: A
authors.lastname: Burny
authors.forename: Carine
authors.initials: C
authors.lastname: Van Lint
mesh_terms: D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins; D002417:Cattle; D004268:DNA-Binding Proteins / Q000502:physiology; D015967:Gene Expression Regulation, Viral; D016356:Gene Products, tax / Q000502:physiology; D001909:Leukemia Virus, Bovine / Q000235:genetics*; D017354:Point Mutation; D011401:Promoter Regions, Genetic; D012756:Sheep; D020079:Terminal Repeat Sequences; D014157:Transcription Factors / Q000502:physiology*; D051720:Upstream Stimulatory Factors
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D004268:DNA-Binding Proteins; D016356:Gene Products, tax; D014157:Transcription Factors; D051720:Upstream Stimulatory Factors