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Electron microscopic visualization indicates that the transcription activator NRI (NTRC) binds with exceptional selectivity and efficiency to a sequence-induced superhelical (spiral) segment inserted upstream of the glnA promoter, accounting for its observed ability to substitute for the natural glnA enhancer. The cooperative binding of NRI to the spiral(More)
Different conformations of polypeptides were characterized by measurements of the circular dichroism (CD) extended into the vacuum ultraviolet region. (i) The linear beta-pleated sheet structure was characterized in a broad ultraviolet region down to 165 nm by examination of copolypeptides composed of alternating hydrophobic and hydrophilic amino-acid(More)
The conformation of the synthetic DNA, poly-[d(A-T)-d(A-T)], has been investigated both in the solid state and in dilute aqueous solutions at different temperatures below its melting point. The change of the circular dichroism (CD) spectra of poly[d(A-T)-d(A-T)] solutions with decreasing temperatures from just below the melting point to 0 degrees involves a(More)
The effect of superhelical constraint on the structure of covalently closed circular DNA (cccDNA; pBR322) with positive and negative writhe (superturn) has been investigated as a function of decreasing and increasing specific linking difference (mean superhelical density sigma). At low and moderate negative superhelical densities sigma, the overall average(More)
Stimulation of transcriptional activity in vitro is observed at low and moderate negative superhelical densities up to the level of the natural superhelical form of the plasmid pBR322. We have isolated and identified three specific transcription products: ampicillinR RNA, tetracyclineR RNA and "Rep" RNA. Their enhancement of transcription occurs at(More)
The structures of poly(dA-dT), poly(dA-dBr5U) and of poly(dA).poly(dT) have been investigated in solution and in fibers, by Raman spectroscopy. Both the alternating poly(dA-dT), poly(dA-dBr5U) and non-alternating poly(dA).poly(dT) exhibit, in the region of sugar phosphate backbone vibrations, two bands of almost equal intensity at about 841 cm-1 and 817(More)