Figure 1.
The Ub conjugation pathway. (A) Ubiquitin (Ub) is first activated and bound by E1 in an ATP-dependent reaction, after which it is transferred to E2. Then, E3 interacts simultaneously with the substrate and the E2-Ub conjugate, facilitating transfer of Ub to the substrate. E3 depicted in (A) is a single subunit which interacts via its RING or U-box domain with E2. An example of a RING-type E3 in JA signaling is DAD1-ACTIVATING FACTOR (DAF) [17]. The HECT-type E3s are not shown. (B) E3 can also occur as a multi-subunit E3 consisting of a CULLIN protein serving as scaffold for an adaptor module that binds the substrate, and the RING domain-containing RBX1 protein that binds E2. An example of a CULLIN-RING ubiquitin ligase (CRL) in JA signaling is SCFCOI1.