LAUSR

Mono-ubiquitination at Lysine 119 of H2A (ubH2A) is a prevalent post-translational modification and associated with gene repression in the context of chromatin. However, the direct function of ubH2A on nucleosome is poorly understood. Here we identify ubH2A's effect on nucleosomes by single-molecular magnetic tweezers. We revealed that ubH2A stabilizes nucleosome by blocking DNA peel-ing from histone octamer. Each ubH2A reinforces one half of the outer wrap and introduces a robust asymmetry for nucleosome unfolding. Furthermore, real-time deubiquitination process con-firmed that ubH2A-nucleosome is sequentially deubiquitinated and restores to unmodified nucleosome state. These results provide a novel mechanism to understand the repression on the passage of RNA or DNA polymerases through the ubH2A-nucleosome barri-er during gene transcription or replication.