[Physico-chemical properties of DNA-dependent RNA-polymerase from Escherichia coli and its subunits].

CD and UV spectroscopy were employed to study at different temperatures the conformational states of the DNA-dependent RNA polymerase core- and holo-enzymes, as well as of its alpha and beta subunits. Both core- and holo-enzyme were shown to have a higher percentage of regular structures than the separate subunits. CD and fluorescence methods were used to monitor the complex formation between rifamycin SV or its derivative, rifampicin, with the RNA polymerase from the E. coli wild and mutant (Rpo B255) types, the former enzyme being sensitive and the latter being resistant to these antibiotics. Complexation led to concomitant changes in the conformation of antibiotics and local structural rearrangements of the protein in vicinity of the binding site which comprises at least one tryptophan residue in a hydrophobic microenvironment.