Source:http://linkedlifedata.com/resource/umls/id/C1514216
NCI: The type of ubiquitin modification determines the functional consequences for the modified protein. Polyubiquitination, which involves chains of usually four or more ubiquitins, typically seen on cytoplasmic proteins, serve as an efficient signal for recognition by the proteasome and subsequent protein degradation. (From PMID and NCI)