Abstract
Ubiquitin-activating enzyme (E1) is the first enzyme in the pathway leading to formation of ubiquitin-protein conjugates. Antibodies raised against E1 were affinity purified and used for immunostaining HeLa cells. Condensed chromosomes in mitotic cells were found to be strongly immunoreactive. Chromosomes from metaphase-arrested HeLa cells were isolated and chromosome-associated proteins were analyzed by Western blotting. E1 was detected in fractions containing isolated chromosomes. These results suggest that E1 is associated with condensed chromosomes during mitosis.