E3 ubiquitin-protein ligase component of the ribosome quality control complex (RQC), a ribosome-associated complex that mediates ubiquitination and extraction of incompletely synthesized nascent chains for proteasomal degradation. Ubiquitination leads to cdc48 recruitment for extraction and degradation of the incomplete translation product. 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. Component of the ribosome quality control complex (RQC), composed of the E3 ubiquitin ligase rkr1/ltn1, rqc1 and mtr1/rqc2, as well as cdc48 and its ubiquitin-binding cofactors. RQC forms a stable complex with 60S ribosomal subunits. Belongs to the LTN1 family.