title: Enhancer functions in U3 of Akv virus: a role for cooperativity of a tandem repeat unit and its flanking DNA sequences.
abstract: cis-Acting transcriptional control elements in the U3 region of the murine retrovirus Akv were analyzed in mouse NIH 3T3 fibroblast cells by using a transient expression vector system based upon a complete long terminal repeat with linked flanking sequences. Deletion analysis pointed to the essential role of sequences within the 99-base-pair direct repeats, and a fragment encompassing the two repeats was found to possess orientation-independent enhancer activity when positioned either upstream or downstream of the transcriptional unit. Removal of one copy of the 99-base-pair repeat led to a reduction in activity of about 2.5-fold when located in an intact U3 environment but to reductions of up to 2 orders of magnitude when placed in other sequence contexts. Our studies of enhancer functions in the presence of one versus two copies of the tandem repeat point to duplicate functions of repeat sequences and sequences flanking the repeat region and emphasize the complex overall organization of this U3 region.
authors.affiliation: Department of Molecular Biology and Plant Physiology, University of Aarhus, Denmark.
authors.forename: S
authors.initials: S
authors.lastname: Lovmand
authors.forename: N O
authors.initials: NO
authors.lastname: Kjeldgaard
authors.forename: P
authors.initials: P
authors.lastname: Jørgensen
authors.forename: F S
authors.initials: FS
authors.lastname: Pedersen
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D004252:DNA Mutational Analysis; D004742:Enhancer Elements, Genetic; D015967:Gene Expression Regulation, Viral; D005822:Genetic Vectors; D066298:In Vitro Techniques; D009052:Leukemia Virus, Murine / Q000235:genetics*; D051379:Mice; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D012045:Regulatory Sequences, Nucleic Acid; D012091:Repetitive Sequences, Nucleic Acid