Transcription of the human beta-globin gene is stimulated by an SV40 enhancer to which it is physically linked but topologically uncoupled.
One postulated mechanism for how the SV40 enhancer stimulates transcription of linked genes involves the enhancer as a binding site for a sequence-specific "gyrase" activity. We sought to test this hypothesis directly by constructing a novel heteroduplex circle, termed a tailed-circle, in which one of the strands contains an extra palindromic sequence base-paired into a hairpin structure. The human beta-globin gene is placed in the circle and the SV40 enhancer on the hairpin tail, where a bound topoisomerase cannot supercoil the circle. Upon transfection of this DNA into HeLa cells the SV40 enhancer on the hairpin arm is still able to stimulate transcription of the beta-globin gene. Southern blot analysis of the DNA after transfection does not demonstrate any repair or replication of the tailed-circle in vivo. These results argue against the sequence-specific gyrase model for SV40 enhancer action.
D004250:DNA Topoisomerases, Type II / Q000378:metabolism*; D004274:DNA, Recombinant / Q000378:metabolism; D004278:DNA, Superhelical / Q000378:metabolism; D004742:Enhancer Elements, Genetic; D005809:Genes, Regulator; D005813:Genes, Synthetic; D005914:Globins / Q000096:biosynthesis* / Q000235:genetics; D006367:HeLa Cells; D006801:Humans; D009690:Nucleic Acid Conformation; D010957:Plasmids; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000235:genetics; D013539:Simian virus 40 / Q000235:genetics*; D014158:Transcription, Genetic
D004274:DNA, Recombinant; D004278:DNA, Superhelical; D011994:Recombinant Proteins; D005914:Globins; D004250:DNA Topoisomerases, Type II