Figure 3 - full size

 

Figure 3.
Fig. 3. The structure of the mutant -resolvase tetramer covalently linked to cleaved DNA. (A) The two site I DNAs (light and dark green, yellow, and orange coils) are cleaved into half sites labeled L, R, L', and R'. S10 (blue and red spheres) in each subunit is covalently linked to the 5' phosphate of adenine 20 (Ade20, green stick). The subunits of the resolvase tetramer (blue, green, red, and magenta) can be divided into two dimers containing antiparallel E helices (L-L' and R-R') or two site I dimers bound to L-R DNA or L'-R' DNA. The D and E helices form a four-helix bundle within the antiparallel dimer. The two antiparallel E helix dimers interact through a flat interface, and the V114 C114 (21) mutation in the E helix crosslinks across the flat interface. The position of the missing phosphates resulting from the use of symmetrized oligos is marked by an orange sphere; its absence does not distort the DNA. (B) The active site at the covalent, cleaved DNA intermediate. A phosphoserine bond formed between Ade20 and S10. R8, D67, R68, and the two nonbridging oxygens of the phosphoserine form a hydrogen-bonding network (blue dashed lines). In the religation step, the free 3'-hydroxyl attacks of the DNA to be exchanged (black arrow) is presumably in line with the phosphoserine bond. (C) A view of the tetramer rotated by 90° from the orientation in (A) shows the packing of four E helices and preceding loops and ß strands.

The above figure is reprinted by permission from the AAAs: Science (2005, 309, 1210-1215) copyright 2005.