Validating maps from single particle electron cryomicroscopy

Progress in single particle cryo-EM, most recently due to the introduction of direct detector devices, has made the high-resolution structure determination of biological assemblies smaller than 500 kDa more routine, but has also increased attention on the need for tools to demonstrate the validity of single particle maps. Although map validation is a continuing subject of research, some consensus has been reached on procedures that reduce model bias and over-fitting during map refinement as well as specific tests that demonstrate map validity. Tilt-pair analysis may be used as a method for demonstrating the consistency at low resolution of a map with image data. For higher-resolution maps, new procedures for more robust resolution assessment and for validating the refinement of atomic coordinate models into single particle maps have been developed.