title: Specific and non specific Escherichia coli ribonucleic acid polymerase DNA complexes are not hydrodynamically equivalent in analytical band sedimentation.
abstract: We have measured the sedimentation coefficients (s) of different DNA molecules of a few thousand base bairs in the presence of increasing amounts of E. coli RNA polymerase under conditions where tight binding complexes are formed. The measured s does not increase linearly with n(n=RNA Polymerase/DNA molar ratio); the s vs n plot can be decomposed into two parts; first the increase in s is small until n reaches a value n0 approximately equal to the number of strong promoters of the DNA molecule under consideration, then when n greater than n0 the slope of s(n) is much higher. The observations are in agreement with a model which postulates that strong specific polymerase binding leads to an increase in frictional coefficient of the RNA Polymerase-DNA complex, while non specific(or less specific)RNAP binding leads to a contraction of the RNA Polymerase-DNA complexes.
mesh_terms: D001665:Binding Sites; D002498:Centrifugation; D004269:DNA, Bacterial / Q000302:isolation & purification*; D012321:DNA-Directed RNA Polymerases / Q000302:isolation & purification*; D004926:Escherichia coli / Q000032:analysis*; D008956:Models, Chemical; D008968:Molecular Conformation
chemical_list: D004269:DNA, Bacterial; D012321:DNA-Directed RNA Polymerases