[Effect of superhelical DNA on the transcription of cloned genes of the T4 phage]

Abstract

The effect of DNA superhelicity on the transcription of T4 DNA fragments containing early genes uvs W, Y and late genes 25-29 was studied. RNA polymerase transcribes both early and late phage genes within the supercoiled recombinant plasmid. Late genes relative transcription increases essentially when T4-modified RNA polymerase is used. DNA relaxation causes a sharp decrease of modified RNA polymerase activity, especially on the late genes. The same effect is obtained in intact cells with recombinant plasmid, which superhelicity is lowered by temperature-sensitive mutation in DNA gyrase. The data obtained prove that DNA superhelicity is required for the T4 late transcription by phage-modified RNA polymerase. It is suggested that the dependence of late transcription on the phage DNA replication in infected cells is connected with phage DNA superspiralization throughout its replication.