title: Proteins from the prokaryotic nucleoid. A protein-protein cross-linking study on the quaternary structure of Escherichia coli DNA-binding protein NS (HU).
abstract: Escherichia coli DNA-binding proteins NS1, NS2 and NS (NS1 + NS2) react with the protein-protein bifunctional cross-linking reagents dimethylsuberimidate and dimethyladipimidate to yield oligomers up to hexamers. The former reagent, with the longer arm, is more efficient than the other shorter one. Both one- and two-dimensional gel electrophoreses show that the cross-linked trimers are homogeneous, while the dimers appear heterogeneous, suggesting that at least two types of dimers but geometrically equivalent trimers are formed. In the presence of DNA, the cross-linking reaction with either reagent yields fewer dimers and more of the larger products. The yield of cross-linked products of various sizes was determined for NS1, NS2 and NS as a function of the protein concentration (0.03-3000 microM). From the results obtained in these experiments, we derived a model of quaternary structure in which dimers and tetramers are predominant in very solutions of the proteins. Above a critical concentration (10-50 microM), interactions among tetramers become increasingly important, yielding octamers and perhaps larger products. Our data do not support a recently proposed model in which the DNA is packaged around a protein disc consisting of 8-10 NS dimers.
mesh_terms: D001426:Bacterial Proteins / Q000302:isolation & purification; D003432:Cross-Linking Reagents; D004268:DNA-Binding Proteins / Q000302:isolation & purification; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000032:analysis*; D046911:Macromolecular Substances; D011485:Protein Binding
chemical_list: D001426:Bacterial Proteins; D003432:Cross-Linking Reagents; D004268:DNA-Binding Proteins; D046911:Macromolecular Substances; C040330:histone-like protein HU, bacteria