Putative E3 ubiquitin-protein ligase involved in the rhizobial infection process. Plays an important role in the early steps of infection thread formation and in growth and differentiation of nodules. 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. Protein modification; protein ubiquitination.