Recombinant cells. Immunofluorescent light micrograph of recombinant COS-9 culture cells expressing the viral gene Large T antigen. Vaults are green, mitochondria are red and cell nuclei are blue. The viral gene causes these cells to produce recombinant protein when instructed to. Vaults are organelles that contain RNA (ribonucleic acid). COS cells are healthy kidney cells from an African green monkey. In immunofluorescence, fluorescent dyes are attached to specific tissues using antibodies. Magnification: x200 at 5x7cm size.