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In many higher organisms, 5%-15% of histone H2A is ubiquitylated at lysine 119 (uH2A). The function of this modification and the factors involved in its establishment, however, are unknown. Here we demonstrate that uH2A occurs on the inactive X chromosome in female mammals and that this correlates with recruitment of Polycomb group (PcG) proteins belonging to Polycomb repressor complex 1 (PRC1). Based on our observations, we tested the role of the PRC1 protein Ring1B and its closely related homolog Ring1A in H2A ubiquitylation. Analysis of Ring1B null embryonic stem (ES) cells revealed extensive depletion of global uH2A levels. On the inactive X chromosome, uH2A was maintained in Ring1A or Ring1B null cells, but not in double knockout cells, demonstrating an overlapping function for these proteins in development. These observations link H2A ubiquitylation, X inactivation, and PRC1 PcG function, suggesting an unanticipated and novel mechanism for chromatin-mediated heritable gene silencing.

Original publication

DOI

10.1016/j.devcel.2004.10.005

Type

Journal article

Journal

Dev Cell

Publication Date

11/2004

Volume

7

Pages

663 - 676

Keywords

Animals, Antibodies, Monoclonal, Blastocyst, Blotting, Western, Carrier Proteins, Cell Line, Crosses, Genetic, Dosage Compensation, Genetic, Embryo, Mammalian, Female, Fibroblasts, Gene Deletion, Gene Silencing, Gene Targeting, Histones, Mice, Mice, Inbred C57BL, Mice, Inbred CBA, Restriction Mapping, Stem Cells, Ubiquitin, rab GTP-Binding Proteins