Tag Team Ubiquitin Ligases

Cullin-RING (CRL) and RING1-IBR-RING2 (RBR) are two distinct types of ubiquitin ligases. In this issue, Scott et al. show that CRLs activate the RBR enzyme ARIH1 to initiate ubiquitin chains on CRL substrates, thereby marking an unexpected and important advance in our understanding of both enzymes.