APC/C-mediated multiple monoubiquitylation provides an alternative degradation signal for cyclin B1

Abstract

The anaphase-promoting complex or cyclosome (APC/C) initiates mitotic exit by ubiquitylating cell-cycle regulators such as cyclin B1 and securin. Lys 48-linked ubiquitin chains represent the canonical signal targeting proteins for degradation by the proteasome, but they are not required for the degradation of cyclin B1. Lys 11-linked ubiquitin chains have been implicated in degradation of APC/C substrates, but the Lys 11-chain-forming E2 UBE2S is not essential for mitotic exit, raising questions about the nature of the ubiquitin signal that targets APC/C substrates for degradation. Here we demonstrate that multiple monoubiquitylation of cyclin B1, catalysed by UBCH10 or UBC4/5, is sufficient to target cyclin B1 for destruction by the proteasome. When the number of ubiquitylatable lysines in cyclin B1 is restricted, Lys 11-linked ubiquitin polymers elaborated by UBE2S become increasingly important. We therefore explain how a substrate that contains multiple ubiquitin acceptor sites confers flexibility in the requirement for particular E2 enzymes in modulating the rate of ubiquitin-dependent proteolysis. Cyclin B is targeted for proteasome-mediated degradation by the E3 ligase APC/C, which is thought to generate polyubiquitin chains for the degradation of mitotic substrates. King and colleagues now demonstrate in Xenopus laevis extracts that multiple monoubiquitylation events are sufficient to target cyclin B1 for degradation.

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Dimova, N., Hathaway, N., Lee, BH. et al. APC/C-mediated multiple monoubiquitylation provides an alternative degradation signal for cyclin B1. Nat Cell Biol 14, 168–176 (2012). https://doi.org/10.1038/ncb2425

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