The role of the helicase loading factors in epigenetic memory

The molecular basis of heterochromatin formation
HP1 is a key constituent of heterochromatin. HP1 promotes chromatin compaction and in this way restricts access of regulatory factors to DNA. Misregulation of the HP1 chromatin interaction is associated with epigenetic disease, cancer and aging. How HP1 binds to chromatin is only partially understood, but of significant biological relevance. HP1 is made up of two conserved domains, the chromo domain and the chromoshadow domain, which are linked by a hinge region. HP1 recruitment to chromatin depends on a chromo domain interaction with a histone H3 that carries a trimethylation mark on lysine 9. However, recently it was found that HP1 recruitment to chromatin also requires the origin recognition complex (ORC) proteins, which usually function in DNA replication. However, how ORC promotes HP1 recruitment to heterochromatin and its molecular function in transcription and role in disease is unknown. We will investigate how ORC proteins influence HP1 recruitment to chromatin and if ORC alters HP1 oligomerisation on chromatin. We will identify structural changes in HP1 in response to ORC binding and in context of the nucleosome. Furthermore, we will analyse the role of the HP1-ORC complex in transcriptional regulation. Finally, we will explore if ORC-HP1 is involved in heterochromatin formation in disease, for example, cancer and Friedreich’s ataxia. These experiments address a key and largely unanswered question in chromatin biology: how is the spreading of heterochromatin regulated? By providing answers to these questions we will obtain a wide ranging understanding of many biological processes including the basis of epigenetic memory, which is disrupted during aging and disease.