Mapping of in vitro transcription units and identification of primary transcripts of the D region of bacteriophage T4

The D region of bacteriophage T4 is comprised of six closely linked genes which are situated between 161 kb and 165 kb on the T4 chromosome. We studied the transcription of these genes in vitro by using DNA templates derived from a series of deletion mutants in this region. The mixture of primary products made by Escherichia coli RNA polymerase were fractionated by gel electrophoresis into discrete RNA species. The results obtained together with the known map positions of the deletions allowed to identify four wild-type and several deletion-specific transcripts of the D region. The end points of these transcripts were approximately mapped. The results demonstrate that the D region has two promoters and two terminators, an organisation which is similar to the previously established organisation of the T4 tRNA gene cluster.