Fig. 3. Profile of SUMO and Ubc9 expression in organotypic cultures of human foreskin keratinocytes. Tissue sections were processed and evaluated for protein expression using antibodies to Ubc9 (A,B), SUMO (B,D), or human keratin 1 (E). For samples B and D, the respective purified proteins (25 µg Ubc9 or 7 µg SUMO1) were included in the primary antibody incubation step to block detection of the corresponding antigens. (F) Negative control where the primary antibody was absent. All sections were counterstained with hematoxylin. Arrows indicate cells expressing high levels of Ubc9. Arrowheads indicate cells in the basal layer exhibiting low levels of Ubc9 expression.