Dynamic O-GlcNAc glycosylation in the brain. Khidekel et al. (p. 339) have developed a method for determining levels of O-GlcNAc modification using quantitative mass spectrometry-based proteomics. The authors found that O-GlcNAc levels at specific protein sites are modulated in neurons and in rat brains in response to stimulation (see also News & Views by Wells, p 303). The cover shows the structure of the translation initiation factor eIF4G, which was found to be glycosylated in neurons, with a chemical model of the O-GlcNAc modification. In the background is an MRI image of a brain. The eIF4G structure is from http://www.pdb.org (PDB ID 1UG3), and the MRI brain image is from the Corbis Corporation (© Allen Bell/Corbis). Cover art by Erin Boyle, based on images provided by Linda Hsieh-Wilson and Peter M. Clark.