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RELION (for REgularised LIkelihood OptimisatioN, pronounce rely-on) is a stand-alone computer program that employs an empirical Bayesian approach to refinement of (multiple) 3D reconstructions or 2D class averages in electron cryo-microscopy (cryo-EM). It is developed in the group of Sjors Scheres at the MRC Laboratory of Molecular Biology. Briefly, the ill-posed problem of 3D-reconstruction is regularised by incorporating prior knowledge: the fact that macromolecular structures are smooth, i.e. they have limited power in the Fourier domain. In the corresponding Bayesian framework, many parameters of a statistical model are learned from the data, which leads to objective and high-quality results without the need for user expertise. The underlying theory is given in Scheres (2012) JMB. A more detailed description of its implementation is given in Scheres (2012) JSB. If RELION is useful in your work, please cite at least one of these papers.

For examples of how we (and some others) have used RELION, see our web site.

Getting started

• Download & install the 1.2 release (also see the list of Known_issues)
• Conventions & File formats
• Tutorial (learn how to use RELION (soon to be updated for 1.3-release))
• Recommended procedures (how we use RELION)
• FAQs (for useful tricks and in case of trouble)

Getting feedback

If you have a question, please first check the FAQs, and secondly whether the topic has been addressed already on the CCP-EM mailing list. If not, please use the CCP-EM list (and not a direct e-mail) to send us your message. It would be helpful to start the subject line of your message with "RELION: "