title: On the role of sulfhydryl groups in the structure and function of the Azotobacter vinelandii RNA polymerase.
abstract: Exposure of sulfhydryl groups as indicated by titration kinetics is decreased under conditions where RNA polymerase exists as a dimer or higher aggregate (low salt), in the presence of Mn2+, or when bound to d(A-T). Incubation of phenylmercurisulfonate with RNA polymerase above pH 9.0 results in loss of d(A-T) binding ability. Poly(U) binding is more sensitive to sulfhydryl modification and is lost as pH's above 8.0. The presence of 4 mM Mn2+ has an obvious effect in stabilizing the polymerase-poly(U) complex when incubated with 10 muM phenylmercurisulfonate + 1 M urea. Incubation of the enzyme with the mercurial and urea results in disaggregation to subprotomeric forms and release of the alpha subunit. Similar treatment in the presence of 4 mM MnSO4 stabilizes the protomeric structure of the enzyme. During chain elongation the enzyme exists as a ternary d(A-T)n-enzyme-r(U-A)n complex in which the bound d(A-T)n is refractory to the destabilizing effect of the mercurial; however, further phosphodiester bond formation is inhibited. The results are defined in terms of a role which reflects the involvement of polymerase sulfhydryl groups in the various conformations necessary for subunit-subunit interaction, tight template binding and catalytic activity.
mesh_terms: D001395:Azotobacter / Q000201:enzymology*; D012321:DNA-Directed RNA Polymerases / Q000032:analysis / Q000378:metabolism*; D004355:Drug Stability; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008345:Manganese / Q000494:pharmacology; D009994:Osmolar Concentration; D011072:Poly U; D011189:Potassium Chloride / Q000494:pharmacology; D011485:Protein Binding; D013438:Sulfhydryl Compounds / Q000032:analysis; D013698:Templates, Genetic
chemical_list: D013438:Sulfhydryl Compounds; D011072:Poly U; D008345:Manganese; D011189:Potassium Chloride; D012321:DNA-Directed RNA Polymerases; D008274:Magnesium