Transcription from plasmid expression vectors is increased up to 14-fold when plasmids are transfected as concatemers

A protocol for increasing transcription from plasmid expression vectors is presented. A vector containing chloramphenicol acetyltransferase (CAT) gene was digested leaving the transcription cassette intact. Heat inactivation of restriction enzymes followed by ligation of the digestion products yielded concatemers which migrated as a single band in agarose gel electrophoresis. Mouse fibroblasts transfected with the concatemers gave a CAT activity that was 14-fold greater than that of cells transfected with a similar mass (equimolar gene number) of the native plasmid. The effect was independent of promoter type, restriction enzyme, number of restriction sites and with a noted exception, cell line.