Association of the episome with metaphase chromosomes. The localization of the episome was studied by FISH on spreads of metaphase chromosomes (A), and the equal distribution of vector molecules was monitored in postmitotic nuclei of dividing cells (B). The episome (green) was visualized by pEPI FISH. To-Pro-3 was used for DNA counterstaining (red). A maximum intensity projection was rendered from a set of 5 mid serial sections in (B). Arrows in (A) indicate a pEPI signal pair, each signal localized on a sister chromatid. For further details see Additional file 4.