1) The overall resolution of the single-particle reconstruction is limited to 4.5A, whereas the entire paper discusses the resulting atomic model as if this were a atomic-resolution structure. Locally the resolution is probably even worse than 4.5A, as for example the β strands are not well separated in Figure 1A. Overall, too little information is given on the quality of the map and the corresponding atomic model. In fact, at 4.5A, the map alone will probably still leave considerable scope for registry or main chain tracing errors. Therefore, the authors should explicitly discuss these caveats where relevant in the main text. In addition, they should provide the following (supplementary?) information in their revision: