title: Physiochemical studies on interactions between DNA and RNA polymerase. Ultraviolet absorption measurements.
abstract: The interaction between Escherichia coli RNA polymerase and a restriction fragment of coliphage T7 DNA containing four promoter sites for the coli enzyme has been studied by difference uv absorption spectroscopy in a low ionic strength buffer containing 10 mm MgCl2 and 50 mM KCl. The binding of the enzyme to the DNA is accompanied by a hyperchromic shift which shows a maximum around 260 nm, and increases with increasing temperature in the temperature range studied (4-40 degrees C). Measurements were also carried out with whole T7 DNA and a restriction fragment containing no promoter site. A comparison of the results obtained with the various DNAs suggests that the binding of an RNA polymerase to a promoter site in the low ionic strength medium causes the disruption of a short segment of the DNA helix, of the order of ten pairs; the binding of an enzyme molecule to a promotor site appears to have a cooperative effect on the binding of the enzyme molecules to adjacent non-promoter sites with concomitant disruption of DNA base pairs.
mesh_terms: D001665:Binding Sites; D003090:Coliphages; D004279:DNA, Viral; D012321:DNA-Directed RNA Polymerases; D004926:Escherichia coli / Q000201:enzymology; D005809:Genes, Regulator; D009691:Nucleic Acid Denaturation; D011485:Protein Binding; D013056:Spectrophotometry, Ultraviolet; D013696:Temperature
chemical_list: D004279:DNA, Viral; D012321:DNA-Directed RNA Polymerases