title: Purification and properties of the Rous sarcoma virus internal enhancer binding factor.
abstract: The internal enhancer binding factor (IBF) that specifically binds sequences within the gag gene internal enhancer of Rous sarcoma virus Schmidt-Ruppin A was purified to near homogeneity from BHK cells. The polypeptides that constituted IBF DNA-binding activity were identified by sodium dodecyl sulfate-polyacrylamide gel analysis. As isolated from BHK cells, IBF consisted of two different but related polypeptides. One (IBF alpha) had a molecular weight of 40,000; the other (IBF beta) had a molecular weight of 20,000 and appeared to be a proteolytic product of IBF alpha. The site within the gag gene to which IBF bounds in vitro (internal enhancer site 2; nucleotides 856 to 878 of the Rous sarcoma virus genome) were demonstrated to function as a cis-acting transcriptional stimulatory element both in vivo and in vitro. By using HeLa cell nuclear transcription extracts, purified IBF was found to function as a trans-acting transcription factor that stimulated transcription in vitro. Purified IBF was also demonstrated to be very similar to EBP20 (K. Carlberg, T. A. Ryden, and K. Beemon, J. Virol. 62:1617-1624, 1988), and it may well belong to the same family of DNA-binding proteins.
authors.affiliation: Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee 37232.
authors.forename: L
authors.initials: L
authors.lastname: Karnitz
authors.forename: D
authors.initials: D
authors.lastname: Poon
authors.forename: P A
authors.initials: PA
authors.lastname: Weil
authors.forename: R
authors.initials: R
authors.lastname: Chalkley
mesh_terms: D000818:Animals; D001358:Avian Sarcoma Viruses / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000302:isolation & purification; D004742:Enhancer Elements, Genetic; D008970:Molecular Weight; D011487:Protein Conformation; D012319:RNA Polymerase II / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics / Q000302:isolation & purification*; D014158:Transcription, Genetic
chemical_list: D004268:DNA-Binding Proteins; D014157:Transcription Factors; D004247:DNA; D012319:RNA Polymerase II