Ribosomal DNA fragments enhance the stability of transfected DNA in Entamoeba histolytica

Genetic manipulation of Entamoeba histolytica is limited by the inability t o express foreign genes at high levels. We tested whether sequences from th e E. histolytica rDNA episome, present in 200 copies per cell, could act to stabilize the episomal transfection vector pTCV1. Ligation of the rDNA tra nscription unit, or sequences downstream of the rDNA transcription unit, in creased pTCV1 copy number and stability and conferred additional zones of D NA replication. Sequences upstream of the rDNA transcription unit dramatica lly destabilized pTCV1. These experiments give additional insights into the mechanism of DNA replication and provide for E. histolytica a set of trans fection vectors with unique properties.