Intellectual Merit: Posttranslational histone modifications, e.g., methylation, acetylation, phosphorylation, and ubiquitination, play central roles in gene regulation in all eukaryotic organisms, determining the active or inactive state of the chromatin. Increasing evidence suggests that many such modifications do not act alone, but function in concert with each other, by a general mechanism known as histone modification crosstalk. One of the major, and perhaps the most interesting, pathways for histone modification crosstalk is the coordination of different histone-modifying enzymatic activities within the same regulator complex, which, in addition to histone-enzyme interactions, involves interactions between the enzymatic components of the regulator complex itself. As an experimental system, this project uses the plant KDM1C-SUVR5-OLD repressor complex. KDM1-based repressors play a key role in regulation of gene expression during such diverse and important processes as acquisition of neuron-specific traits in mammals and determination of flower timing in plants. Of all such repressors known to date, both in plants and animals, the plant KDM1C-SUVR5-OLD1 complex is unique because it contains a deubiquitinase activity, which has never before been observed associated with KDM1, and because one enzymatic activity (OLD1) depends on another (SUVR5). The project, therefore, aims to uncover aspects of chromatin-modifying repressor complexes that have not been observed in other model systems. This is achieved by pursuing two focused specific aims: (i) biochemical characterization of the KDM1C-SUVR5-OLD1 complex, and (ii) identification and initial characterization of a protein interaction network for activity of the KDM1C-SUVR5-OLD1 complex. Broader Impacts: The research is integrated into the teaching of science at the junior educational level, focusing on undergraduate students, who work on the projects and learn scientific thinking and modern experimentation. Specifically, the project anticipates involvement of three undergraduate students, who usually include underrepresented minorities recruited both from Stony Brook and via partnerships with Hunter College and Lehman College in New York City. In addition, the project aims to train high school teachers via Stony Brook?s Center for Science and Mathematics Education (CESAME), where the PI will teach a series of seminars and a summer workshop on epigenetics based on the concepts and results of this research. Finally, the project will train a postdoc to prepare this individual for an independent career in academia, biotech industry and/or Government agencies. Thus, this project promotes proactive outreach activities, which recruit students into the science pipeline, prepare beginning scientists for independent careers, and inform the public about science and technology.