The RING domain of RING Finger 11 (RNF11) protein binds Ubc13 and inhibits formation of polyubiquitin chains.

The Really Interesting New Gene (RING) Finger protein 11 (RNF11) is a subunit of the A20 ubiquitin-editing complex that ensures the transient nature of inflammatory responses. Although the role of RNF11 as a negative regulator of NF-κB signalling is well-documented, the molecular mechanisms that underpin this function are poorly understood. Here, we show that RNF11 binds both Ubc13 and the Ubc13~ubiquitin conjugate tightly and with similar affinity, but has minimal E3 ligase activity. Remarkably, RNF11 appears to bind Ubc13 so tightly that it outcompetes the E1 and an active E3 ligase. As a consequence, RNF11 may regulate the activity of E3s that rely on Ubc13 for ubiquitin chain assembly by limiting the availability of Ubc13 and its conjugate.