Spatial arrangement of DNA-dependent RNA polymerase of Escherichia coli and DNA in the specific complex. A neutron small angle scattering study.

In this paper we demonstrate that neutron small angle scattering is a suitable method to study the spatial arrangement of large specific protein-DNA complexes. We studied the complex of DNA-dependent RNA polymerase of Escherichia coli and a 130 base-pair DNA fragment containing the strong promoter A1 of bacteriophage T7. Contrast variation of the complex with deuterium allowed us to "visualize" either RNA polymerase, or DNA, or both components in situ.

Solution structure of a short DNA fragment studied by neutron scattering.

The solution structure of a DNA fragment of 130 base pairs and known sequence has been investigated by neutron small-angle scattering. In 0.1 M NaCl, the overall structure of the DNA fragment which contains the strong promoter A1 of the Escherichia coli phage T7 agrees with that expected for B-DNA.

Deuterium incorporation into Escherichia coli proteins. A neutron-scattering study of DNA-dependent RNA polymerase.

Neutron small-angle scattering studies of single protein subunits in a protein-DNA complex require the adjustment of the neutron scattering-length densities of protein and DNA, which is attainable by specific deuteration of the protein. The neutron scattering densities of unlabelled DNA and DNA-dependent RNA polymerase of Escherichia coli match when RNA polymerase is isolated from cells grown in a medium containing 46% D2O and unlabelled glucose as carbon source. Their contrasts vanish simultaneously in a dialysis buffer containing 65% D2O.

Characterization of a half-molecular fragment obtained by reduction of human alpha 2-macroglobulin with dithiothreitol. A small-angle X-ray and neutron scattering investigation.

A half-molecular fragment of alpha 2-macroglobulin has been prepared by reducing and alkylating the inter-subunit disulfide bonds in the tetrameric alpha 2-macroglobulin molecule with 1 mM dithiothreitol (40 min) and 3 mM iodoacetamide (40 min). Further purification was made by gel chromatography and the homogeneous population of half-molecules has been characterized by the techniques of small-angle X-ray and neutron scattering. The radii of gyration found by the two methods are 57.