E3 ubiquitin-protein ligase that promotes the ubiquitination and proteasomal degradation of KRP1 and KRP2. S-ubiquitinyl-[E2 ubiquitin-conjugating enzyme]-L-cysteine + [acceptor protein]-L-lysine = [E2 ubiquitin-conjugating enzyme]-L-cysteine + N(6)-ubiquitinyl-[acceptor protein]-L-lysine. A number of isoforms are produced. According to EST sequences. Induced by the beet severe curly top virus (BSCTV) C4 protein and by BSCTV infection. No defects in growth and development, but reduced susceptibility to beet severe curly top virus infection. Favors geminivirus replication by up-regulating the host cell cycle.