Enhancement and inhibition of DNA transcriptional activity by spermine: A marked difference between linear and circular templates

We compared the transcriptional activities of the circular and linear forms of short (4 kbp) and giant (106 kbp) DNA molecules in the presence of a polyamine, spermine (4+). With an increase in the spermine concentration, transcriptional activity was enhanced, followed by an inhibitory effect, and complete inhibition was observed in the sole case of long, linear templates. A difference between the transcriptional properties of circular and linear conformations is found for giant DNA molecules. These results are discussed in relation to DNA conformational transitions.