PMID:1370623
| Citation |
Geiselmann, J, Yager, TD, Gill, SC, Calmettes, P and von Hippel, PH (1992) Physical properties of the Escherichia coli transcription termination factor rho. 1. Association states and geometry of the rho hexamer. Biochemistry 31:111-21 |
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| Abstract |
To function as a DNA-RNA helicase in rho-dependent transcript termination, six genetically identical subunits of the Escherichia coli transcription termination protein rho must first assemble into a hexameric complex. To help determine the quaternary structure of this complex, we have studied the association equilibria of the rho protomers. Sedimentation equilibrium, sedimentation velocity, diffusion, X-ray scattering, and neutron-scattering data have been combined to create a "phase diagram" of the association states of this protein as a function of protein concentration and ionic environment. The results show that rho exists predominantly as a hexamer under approximately physiological conditions and that this hexamer is in equilibrium with both lower and higher states of association that may also have physiological relevance. Small-angle X-ray scattering measurements and theoretical calculations indicate that the rho hexamer has a radius of gyration of 50 +/- 3 A. The radius of gyration measured by small-angle neutron scattering in 2H2O is 47 +/- 3 A. These scattering studies also support earlier models of rho as a planar hexagon which have been developed on the basis of electron microscopy. In the following paper in this issue [Geiselmann, J., Seifried, S. E., Yager, T. D., Liang, C., & von Hippel, P. H. (1992)], these results are combined with information on symmetry, subunit interactions, and packing geometry to obtain a model of the quaternary structure of the functional rho hexamer. |
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| Keywords |
DNA/metabolism; Diffusion; Escherichia coli/chemistry; Ligands; Mathematics; Models, Molecular; Molecular Weight; Multienzyme Complexes/metabolism; Oligonucleotides/metabolism; Protein Binding; Protein Conformation; RNA/metabolism; Rho Factor/chemistry; Rho Factor/genetics; Rho Factor/isolation & purification; Salts/metabolism; Scattering, Radiation; Structure-Activity Relationship; Transcription, Genetic; Ultracentrifugation; X-Ray Diffraction |
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