The matching of physical models to three-dimensional electron-density maps: A simple optical device

A simple device is described which permits the optical superposition of skeleton atomic models and three-dimensional electron-density maps. The model of a globular protein can be built directly “into the map”. No measurements of coordinates are required during construction, and the quality of the fit can be assessed easily. Photographs taken with this device may be useful in presenting the interpretation of electron-density maps in a form easily...