Cryogenic electron microscopy (cryo-EM) maps are now at the point where resolvability of individual atoms can be achieved. However, resolvability is not necessarily uniform throughout the map. We introduce a quantitative parameter to characterize the resolvability of individual atoms in cryo-EM maps, the map Q-score. Q-scores can be calculated for atoms in proteins, nucleic acids, water, ligands and other solvent atoms, using models fitted to or derived from cryo-EM maps. Q-scores can also be averaged to represent larger features such as entire residues and nucleotides. Averaged over entire models, Q-scores correlate very well with the estimated resolution of cryo-EM maps for both protein and RNA. Assuming the models they are calculated from are well fitted to the map, Q-scores can be used as a measure of resolvability in cryo-EM maps at various scales, from entire macromolecules down to individual atoms. Q-score analysis of multiple cryo-EM maps of the same proteins derived from different laboratories confirms the reproducibility of structural features from side chains down to water and ion atoms.

低温电子显微镜（cryo-EM）图现在可以实现单个原子的可分辨性。但是，可解析性不一定在整个地图中是一致的。我们引入了一个定量参数来表征低温电磁图中单个原子的可分辨性，即图Q分数。可以使用拟合或源自低温电磁图的模型计算蛋白质、核酸、水、配体和其他溶剂原子中的原子的Q分数。Q- scores 也可以被平均来表示更大的特征，例如完整的残基和核苷酸。整个模型的平均值，Q- 分数与蛋白质和 RNA 的冷冻电镜图的估计分辨率非常相关。假设计算它们的模型与地图非常吻合，Q- scores 可用于衡量从整个大分子到单个原子的各种尺度的低温 EM 地图的可分辨性。来自不同实验室的相同蛋白质的多个低温 EM 图的Q分数分析证实了从侧链到水和离子原子的结构特征的可重复性。