FIGURE 5.

Comparison of SecA·SecY photocross-linking results with front-to-front and back-to-back SecA·SecYEG models. Front-to-front (A) and back-to-back (B) models of SecA·SecYEG were generated from the T. maritima SecA·SecYEG crystal structure (38) as described under “Experimental Procedures.” SecA and SecYEG are depicted in colored ribbons as described in the Fig. 3 legend except that the two SecY molecules are shown in light yellow or light gray to better highlight the different orientations. SecA residues that were positive or negative for cross-linking to SecY are shown as pink or yellow balls, respectively. The red rectangle outlines the NBD-I-NBD-II half of SecA, whose SecY-reactive resides are better accommodated by the front-to-front orientation of the SecYEG homodimer.