Source:http://linkedlifedata.com/resource/umls/id/C1513486
NCI: The type of ubiquitin modification determines the functional consequences for the modified protein. Monoubiquitination does not serve as a proteasome targeting signal, but plays other distinct roles. Target proteins are monoubiquitinated on one or more lysine residues, which serve as a signal for intracellular sorting as well as endocytosis of cell-surface proteins. Monoubiquitination of cell-surface receptors serves as a signal to target them to lysosome, where they are degraded by lysosomal proteases. (From PMID and NCI)