Protein function is dynamically regulated in the cell by reversible posttranslational modifications. We are interested in the mechanism by which chromatin modifications regulate transcription, nucleosome dynamics and the response to DNA damage. A particular focus is on the non-degradative signaling played by the attachment of the small protein, ubiquitin, to histone proteins. We study the role that ubiquitination plays in these processes and on the mechanism of cross-talk between histone ubiquitination, acetylation and methylation, which together orchestrate the complex events underlying mRNA transcription and DNA repair. We use a combination of cryo-electron microscopy, x-ray crystallography, solution biochemistry, cell-based assays, and a variety of biophysical tools to gain insights into the mechanisms underlying these essential cellular processes.