FIG. 8.
Crystal structure of a RecBCD-DNA initiation complex. (A) The RecBCD-DNA complex. Alpha-helices are shown as cylinders, and beta-sheets are shown as arrows. The color scheme is the same as that in the primary structure diagram (Fig. 4). The helicase domain of RecB (RecBHel) is shown in red, and the nuclease domain (RecBNuc) is in magenta. RecC is in blue, RecD is in green, and the hairpin DNA substrate is in orange. The hairpin end of the DNA is not visible, as it is disordered in the structure, but would occupy the space to the left of the DNA end as shown here. (B) Cutaway view of the RecBCD-DNA complex showing the tunnels running through the complex. The color scheme is described above. The protein is shown as a space-filling model, which has been cut back (dark surfaces) to reveal the ssDNA tails in the tunnel entrances. The DNA substrate has not been cut away and is shown as a partially transparent space-filling model. Architectural features on the path of the ssDNA strands as they are pulled through the complex are highlighted (see the text for details).