Efficient Supercoiling of DNA by a Single Condensin Complex as Revealed by Electron Spectroscopic Imaging  David P Bazett-Jones, Keiji Kimura, Tatsuya Hirano  Molecular Cell  Volume 9, Issue 6, Pages 1183-1190 (June 2002) DOI: 10.1016/S1097-2765(02)00546-4

Figure 1 Stoichiometric Relationships between Protein and Nucleic Acid in the Condensin-DNA Complexes Total molecular mass of the complexes was measured from a mass-sensitive image recorded at an energy loss of 120 eV. DNA content was calculated from the net phosphorus signal that had been obtained by division of the phosphorus postedge (155 eV) by the preedge image (120 eV). Protein content was calculated from the difference of the DNA content and the total molecular mass. The DNA and protein content were plotted for complexes formed in the presence of ATP (top), AMP-PNP (middle), or no nucleotide (bottom). Molecular Cell 2002 9, 1183-1190DOI: (10.1016/S1097-2765(02)00546-4)

Figure 2 Electron Spectroscopic Imaging of the Condensin-DNA Complexes Purified condensin was incubated with relaxed circular DNA in the presence of ATP (A), AMP-PNP (B), or no nucleotide (C). Alternatively, a nicked circular DNA was used as a substrate in the presence of ATP (D). Bar, 130 nm. Histograms show the average numbers of crossovers observed in the protein-free region of DNA under the different conditions (E). Molecular Cell 2002 9, 1183-1190DOI: (10.1016/S1097-2765(02)00546-4)

Figure 3 Phosphorus Images of DNA Present in the Condensin-DNA Complexes Images were captured in the presence of ATP (A) or AMP-PNP (B). Arrows show two protrusions of phosphorus, indicative of two DNA gyres around a protein core. Such organized structures are observed in the presence of ATP (A), but not in the presence of AMP-PNP (B). Line scans of the respective phosphorus maps of the complexes are shown at the right. The start and end points of the scans are indicated by Xs in (A) and (B). The scans were two pixels wide, with the average value represented. The average of 16 net phosphorus images displaying a similar orientation is shown in (C). A horizontally scanned profile of this image was obtained with a bar of two pixels wide, which was drawn between the top pair of Xs (left). Alternatively, the average of several horizontal scans was obtained in the region between the top and middle pairs of Xs (center) or in the region between the top and bottom pairs of Xs (right). Scale bar, 10 nm in (A) and (B), and 4 nm in (C). Molecular Cell 2002 9, 1183-1190DOI: (10.1016/S1097-2765(02)00546-4)

Figure 4 Overlays of Mass-Sensitive and Net Phosphorus Images Mass-sensitive energy-filtered images recorded at 120 eV (black and white, left), net phosphorus images (red, middle), and superposition of net phosphorus (red) on mass-sensitive images (green, right). Condensin-DNA complexes were formed in the presence of ATP (A) or AMP-PNP (B). Bar, 10 nm. Molecular Cell 2002 9, 1183-1190DOI: (10.1016/S1097-2765(02)00546-4)

Figure 5 A Model for DNA Supercoiling Driven by Condensin A single condensin complex (shown by the two-armed, symmetrical molecule) can introduce two positive gyres of DNA in its bound region. The resulting superhelical tension produces two compensatory-negative supercoils in the protein-free region of DNA. One possibility is that the two globular domains of the SMC subunits (∼7 nm in diameter) wrap DNA, creating the two positive gyres (∼12 nm in outer diameter) whose relative orientation is fixed into a right-handed solenoidal form. The relative size of DNA and condensin is shown arbitrarily. For simplicity, the non-SMC subunits of condensin were omitted from the diagram. Molecular Cell 2002 9, 1183-1190DOI: (10.1016/S1097-2765(02)00546-4)