The E3 Ligase CUL3/RDX Controls Centromere Maintenance by Ubiquitylating and Stabilizing CENP-A in a CAL1-Dependent Manner

• The CENP-A loading factor CAL1 interacts with the E3 ligase adaptor RDX
• CAL1’s interaction with RDX is required for correct chromosome segregation
• CENP-A is ubiquitylated by CUL3/RDX only in the presence of CAL1
• CUL3/RDX ubiquitylation of CENP-A mediates the stability of CENP-A and CAL1

SummaryCentromeres are defined by the presence of the histone H3 variant CENP-A in a subset of centromeric nucleosomes. CENP-A deposition to centromeres depends on a specialized loading factor from yeast to humans that is called CAL1 in Drosophila. Here, we show that CAL1 directly interacts with RDX, an adaptor for CUL3-mediated ubiquitylation. However, CAL1 is not a substrate of the CUL3/RDX ligase but functions as an additional substrate-specifying factor for the CUL3/RDX-mediated ubiquitylation of CENP-A. Remarkably, ubiquitylation of CENP-A by CUL3/RDX does not trigger its degradation but stabilizes CENP-A and CAL1. Loss of RDX leads to a rapid degradation of CAL1 and CENP-A and to massive chromosome segregation defects during development. Essentially, we identified a proteolysis-independent role of ubiquitin conjugation in centromere regulation that is essential for the maintenance of the centromere-defining protein CENP-A and its loading factor CAL1.

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