(a) Structure of oriP/EBNA-1 vectors. The scheme represents a frataxin expression plasmid-containing episomal elements (oriP/EBNA-1). (b) orP/EBNA-1 plasmids remain as stable replicating, nonintegrating episomes within nuclei of interphase (and postmitotic) cells. (c) oriP/EBNA-1 episomes attach to the periphery of chromosomes through EBNA-1 protein and segregate during mitosis.