Transcription of DNA injected into Xenopus oocytes is influenced by template topology

We have assayed the transcription of the herpes simplex virus thymidine kinase gene on circular and linear plasmids after injection into Xenopus oocytes. The circular plasmids appear to be transcribed at least 500 times more efficiently than the linear plasmids. Moreover, when the circular templates are allowed to form functioning transcription complexes, and are then linearized in situ, the synthesis of accurate transcripts is substantially reduced.