Deoxyribonucleic acidgyrase-deoxyribonucleic acid complex containing 140 base pairs of deoxyribonucleic acid and an .alpha.2.beta.2 protein core

Abstract

Staphylococcal nuclease digestion of the complex between DNA and [Micrococcus luteus] DNA gyrase yields a gyrase-DNA core particle composed of a 140 base pair DNA segment and an active gyrase enzyme. The partial specific volume and s20,w [sedimentation coefficient in water at 20.degree. C] of this purified core complex are measured to be 0.70 cm3/g and 14.5 S, respectively, by sedimentation measurements in H2O and D2O media. The MW of the core complex estimated from equilibrium centrifugation is 470,000; the ratio of the translational frictional coefficient to that of the unsolvated equivalent sphere is calculated to be 1.9. Treatment of free gyrase in solution with dimethyl suberimidate gives 3 cross-linked species of roughly equal amounts that can be identified as .alpha.2, .alpha.2.beta. and .alpha.2.beta.2. When the gyrase core complex is treated with the same cross-linking agent, 70-80% of the protein is converted to the .alpha.2.beta.2 species. These results establish that the gyrase-DNA core complex contains a 140 base pair DNA segment and a tetrameric .alpha.2.beta.2 protein.