DNA binding reorganizes the intrinsically disordered C-terminal region of PSC in Drosophila PRC1

ABSTRACT: Polycomb Group (PcG) proteins regulate gene expression by modifying chromatin. A key PcG complex, PRC1, has two activities: a ubiquitin ligase activity for histone H2A, and a chromatin compacting/nucleosome bridging activity that can inhibit transcription and chromatin remodeling. In Drosophila, the Posterior Sex Combs (PSC) subunit of PRC1 is central to both activities. The N-terminal homology region (HR) of PSC partners with dRING to form the ubiquitin ligase, while its intrinsically disordered C-terminal region (PSC-CTR) compacts chromatin, and inhibits chromatin remodeling and transcription in vitro. Both the HR and the PSC-CTR are essential in vivo. To understand how these two activities may be coordinated in PRC1, we used cross-linking mass spectrometry (XL-MS) to analyze the conformations of the PSC-CTR in PRC1 and how they change on binding DNA. XL-MS identifies interactions between the PSC-CTR and the core of PRC1, including the PSC HR. New contacts and overall more compacted PSC-CTR conformations are induced by DNA binding. We used chemical acetylation of accessible lysines for MS-based protein footprinting of the PSC-CTR. Protein footprinting reveals an extended, bipartite candidate DNA/chromatin binding surface. Our data suggest a model in which DNA (or chromatin) follows a long path on the flexible PSC-CTR. Intramolecular interactions of the PSC-CTR detected by XL-MS can bring the high affinity DNA/chromatin binding region close to the core of PRC1 without disrupting the interface between the ubiquitin ligase and the nucleosome. Our approach may be applicable to understanding the global organization of other large IDRs that bind nucleic acids.

INSTRUMENT(S): Orbitrap Fusion

ORGANISM(S): Drosophila Melanogaster (ncbitaxon:7227)

SUBMITTER: Nicole J Francis  

PROVIDER: MSV000085418 | MassIVE | Fri May 15 13:55:00 BST 2020

REPOSITORIES: MassIVE