DNA topology regulates rat prolactin gene transcription

A cell-free transcription system was used to examine the effects of DNA negative supercoiling on transcription from rat prolactin promoters. The mRNA was faithfully transcribed from prolactin promoters that contained the DNA fragment spanning from -1960 to -10 base pairs upstream of the prolactin transcription start site. Prolactin promoters in supercoiled form, prepared from Escherichia coli, have a higher transcriptional efficiency than the promoter in the relaxed form. Deletion of DNA sequences containing the estrogen response element and putative non-B form DNA elements from the upstream region of the prolactin gene did not alter this effect of DNA topology on prolactin transcription. We further separated transcription into preinitiation and elongation steps by using sarkosyl and found that more preinitiation complexes were assembled on the supercoiled prolactin promoters than on the relaxed promoters. DNA supercoiling therefore plays an important role in controlling prolactin gene expression by facilitating the formation of preinitiation complexes on the promoters.