The SAGA of removing nucleosomal ubiquitin Covalent modifications of histones play a critical role in gene regulation. The addition of the small protein ubiquitin to histone H2B in nucleosomes is a mark of actively transcribed chromatin. Morgan et al. determined the crystal structure of a nucleosome bound by a module of the SAGA protein complex that removes ubiquitin from histone H2B (see the Perspective by Workman). The structure suggests that the deubiquitinating module can remove ubiquitin at multiple points during the transcription cycle. Science , this issue p. 725 ; see also p. 667