RELION, for REgularized LIkelihood OptimizatioN, is an open-source computer program for
the refinement of macromolecular structures by single-particle analysis of electron cryo-
microscopy (cryo-EM) data. Whereas alternative approaches often rely on user expertise for
the tuning of parameters, RELION uses a Bayesian approach to infer parameters of a
statistical model from the data. This paper describes developments that reduce the
computational costs of the underlying maximum a posteriori (MAP) algorithm, as well as …