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Efficient repression of the two promoters P1 and P2 of the gal operon requires the formation of a DNA loop encompassing the promoters. In vitro, DNA looping-mediated repression involves binding of the Gal repressor (GalR) to two gal operators (OE and OI) and binding of the histone-like protein HU to a specific locus (hbs) about the midpoint between OE and OI, and supercoiled DNA. Without DNA looping, GalR binding to OE partially represses P1 and stimulates P2. We investigated the requirement for DNA supercoiling and HU in repression of the gal promoters in vivo in strains containing a fusion of a reporter gene, gusA or lacZ, to each promoter individually. While the P1 promoter was found to be repressible in the absence of DNA supercoiling and HU, the repression of P2 was entirely dependent upon DNA supercoiling in vivo. The P2 promoter was fully derepressed when supercoiling was inhibited by the addition of coumermycin in cells. P2, but not P1, was also totally derepressed by the absence of HU or the OI operator. From these results, we propose that the repression of the gal promoters in vivo is mediated by the formation of a higher order DNA-multiprotein complex containing GalR, HU and supercoiled DNA. In the absence of this complex, P1 but not P2 is still repressed by GalR binding to OE. The specific nucleoprotein complexes involving histone-like proteins, which repress promoter activity while remaining sensitive to inducing signals, as discussed, may occur more generally in bacterial nucleoids. 相似文献
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Nishi H Senoo M Nishi KH Murphy B Rikiyama T Matsumura Y Habu S Johnson AC 《The Journal of biological chemistry》2001,276(45):41717-41724
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Binding of the herpes simplex virus immediate-early gene product ICP4 to its own transcription start site 总被引:72,自引:51,他引:21 下载免费PDF全文
M T Muller 《Journal of virology》1987,61(3):858-865
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A human TATA binding protein-related protein with altered DNA binding specificity inhibits transcription from multiple promoters and activators. 下载免费PDF全文
Paul A. Moore Josef Ozer Moreh Salunek Gwenael Jan Dennis Zerby Susan Campbell Paul M. Lieberman 《Molecular and cellular biology》1999,19(11):7610-7620
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