Research Interests
Our lab studies the role of chromatin in the regulation of transcription and the repair of DNA double strand breaks, using budding yeast Saccharomyces cerevisiae as a model system. Chromatin is a polymer of protein and DNA, in which the major repeating unit is the nucleosome. The nucleosome is an octamer of four histone proteins – two H2A-H2B dimers and one H3-H4 tetramer – around which is wrapped 147 bp of DNA in ~2 superhelical turns. The nucleosomal structure of chromatin is inhibitory to the access of proteins to DNA, but eukaryotic cells have evolved a number of mechanisms to surmount this barrier. One mechanism involves the post-translational modification of histones, which includes acetylation, methylation, phosphorylation, and ubiquitylation of residues that are primarily located in the N terminal extensions that protrude from the body of the nucleosome core.
Our lab is interested in the regulation and cellular roles of histone H2B ubiquitylation. In contrast to most other histone modifications, which involve small chemical modifications on the histone N termini, the monoubiquitylation of H2B results in the placement of a 76 amino acid protein that is half the size of a histone on the C-terminus of H2B. H2B ubiquitylation is evolutionarily conserved and regulated by the enzymes Rad6, a ubiquitin conjugating enzyme, Bre1, a ubiquitin ligase, two ubiquitin proteases, Ubp8 and Ubp10, and a number of factors with known roles in transcription initiation and elongation. In collaboration with the labs of Shelley Berger at the Wistar Institute and Brian Strahl at the University of North Carolina, we have shown that H2B ubiquitylation (H2Bub) is co-transcriptionally regulated, leading to the dynamic ubiquitylation and deubiquitylation of H2B over gene coding regions as RNA polymerase II (Pol II) elongates. Our recent studies have focused on the role of H2Bub in nucleosome dynamics during transcription elongation. We have found that H2Bub co-operates with the histone chaperone Spt16 to reassemble nucleosomes that are displaced by the passage of Pol II and thus restore chromatin structure. Our current research is directed at defining the potential roles of H2Bub and Spt16 in restarting stalled or blocked DNA replication forks. We believe that the presence of H2Bub, in conjunction with histone chaperones, plays a general role in the maintenance of genome integrity by stabilizing nucleosomes. In addition, we have also initiated a study to define the role of H2Bub during the entry and exit from stationary phase, an excellent model for cellular quiescence. We are focusing on the signal transduction pathways and factors that regulate the de-ubiquitylation and re-ubiquitylation of H2B during these phases of the yeast life cycle, which will provide insight into environmental signalling to histone modifications.
A second mechanism to alter chromatin structure is through the ATP-dependent disruption of histone-DNA contacts, which can lead to nucleosome sliding on the chromatin fiber or even nucleosome displacement. Our lab focuses on the role of factors that promote such nucleosome remodeling during the repair of DNA double strand-breaks (DSBs). We have found that nucleosome remodeling by the INO80 complex promotes nucleosome eviction around a defined DSB, and that this event promotes the rapid recruitment of factors that repair DSBs. Our current research is drected at identifying and functionally characterizing the patterns of histone modifications and nucleosome positions around a DSB and the sequences that repair the DSB by homologous recombination.
Information about post-doctoral positions in the Osley lab.
Selected Publications
Link to PubMedCurrent Lab Members:
Mary Ann Osley, PHD, Principal Investigator
Toyoko Tsukuda, PhD, Senior Staff Associate
Kelly M. Trujillo, PhD, Postdoctoral Fellow
Cory Hillyer, BS, Research Technician
Myrriah S. Chavez, BS, Research Technician
Diego Ramallo-Pardo, BS, Visiting Scientist
Past Lab Members:
Cheng-Fu Kao, PHD, Academia Sinica, Taiwan
Alastair Fleming, PhD, Glasgow University
Dana Underwood, PhD, Central NM CC
