Bovine pulmonary artery endothelial cell labeled with probes for mitochondria and the phosphorylated form of histone H3. Phosphorylated histone H3 was detected using a rabbit anti–phosphohistone H3 antibody prelabeled with the Zenon® Alexa Fluor® 555 Rabbit IgG Labeling Kit (Cat. no. Z25305). Endogenous biotin in the mitochondria was labeled using streptavidin (Cat. no. S888) followed by a rabbit anti-streptavidin antibody prelabeled with the Zenon® Alexa Fluor® 488 Rabbit IgG Labeling Kit (Cat. no. Z25302).