Immunoelectron microscopic localization of ubiquitin in hepatoma cells.

Abstract
Ubiquitin, a 76 amino acid protein, is covalently attached to abnormal and short‐lived proteins, thus marking them for ATP‐dependent proteolysis in eukaryotic cells. Free (unconjugated) ubiquitin was localized in hepatoma cells using affinity purified anti‐ubiquitin antibodies and colloidal gold immunoelectron microscopy. The anti‐ubiquitin antibodies recognize only unconjugated ubiquitin. Ubiquitin is found within the cytoplasm, nucleus, the microvilli, autophagic vacuoles and lysosomes.