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.
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.
Calomme
Claire
C
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.
Nguyen
Thi Lien-Anh
TL
de Launoit
Yvan
Y
Kiermer
Veronique
V
Droogmans
Louis
L
Burny
Arsene
A
Van Lint
Carine
C
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
D051792:Basic Helix-Loop-Helix Proteins; D004268:DNA-Binding Proteins; D016356:Gene Products, tax; D014157:Transcription Factors; D051720:Upstream Stimulatory Factors