Abstract
T antigen was localized in simian virus 40 lytically infected and transformed cells by Fab' antibody conjugates at the ultrastructural level. This virus-specific protein appeared in the cytoplasm of permissive cells as early as 3 h after infection. At later time intervals, the T antigen was localized in both the cytoplasm and nucleus and finally (24 h) in the nucleus. These results suggest a synthesis of T antigen on cytoplasmic ribosomes, with subsequent transfer to the nucleus.